Likely because by this point it fell into a legal area of trademark law known as Gerneric Trademark. In many jurisdictions, a product can be said to become a generic product when no other unique name exists for a generic version of the product. This occurs usually generic competators can make the same products and market them with names similar to the brand name products because no such off brand name exists for a competator to use. It's quite common in medicine, where the brand name first product on the market is the best way to describe the medicine used. Famously Asprine (acetylsalicylic acid) and Heroin (diacetylmorphine) were originally trademarked by Bayer, a pharmacutical company before being declared the generic name for the product (in the case of Heroine, Bayer lost the trademark as part of the Treaty of Versailles. Asprin is generic in the U.S. but still protected in many countries.).
For non-medical companies, the Escalator (trademarked by Otis Elevator Company) is now used for any moving stairway regardless of manufacture. Other non-medicinal products include "Flip Phone," "Laundromat," "Trampoline," and "Videotape."
For other situations, the trademark may still hold, but the public uses the brand name as if it was the generic term. The companies retain the trademark and may persue trademark infringement but will often not because sometimes it's free advertising. Examples of these include "Band-Aid" (generic: Adhesive Bandage), "Bubble Wrap" (generic: Inflated Cushioning), "Jell-o" (Gelatin desert), "Popsicle" (Ice pop), "Frisbee" (Flying Disk), "Taser" (Stun Gun), and "Zamboni" (Ice Resurfacer).
In some cases a company might not persue the trademark violations because there is the risk that the courts can rule the trademark name is infact generic, thus taking away their right to use the term, and more importantly, the free advertising. For example, if a character in a tv-show discusses "Jell-o" instead of a Gelatine Desert, Kraft Food (the trademark owners) do still win because it's free advertising for their product over a competor's brand. Sure, any modern Bill Cosby mockery will inevitably lead to use of the phrase "With the Quaaludes in the Jell-o Pudding Pop" which is not the Kraft Food prefered use of their product, but Cosby is no longer the spokes person for Jell-o products, and Kraft's marketing and legal teams are wise enough to know that it's going to do more damage to fight the jokes than it would be to just roll with it as free promotion for their product in any comedy club in the country AND that most commedians are mocking Cosby's horrific acts despite, not advocating for the combination of Jell-o and sedatives and the audience tends to understand this.
Like the trademarked phrase of "Taco Tuesday" isn't fought because the phrase is widely said by people all over the world... but legally only one company can advertise a promotional deal with the phrase "Taco Tuesday". The trademark holders won't fight it unless they have a real reward to go with that risk... say if Taco-Bell didn't know they can't say "Taco Tuesday."
Edit: According to the article you linked, the suit in 2019 was against another chain was giving a promotional deal called "Taco Tuesday" which violates Taco John's trademarked promotional deal "Taco Tuesday". Lebron's attempt to trademark the phrase was for use in podcasts in online media to protect his use of the phrase when posting podcasts of his family having Tacos for dinner on Tuesday nights. His attempted Trademark is fundamentally different than Taco Johns, which is a specific promotional deal. Lebron and John are not competing in Taco Eateries... they're selling two different products. A phrase or word is not in and of itself protected.
I could apply for a Trademark for a greenhouse gardening store that, as a quirk, highers exclusively men with a large amount of body hair, facial hair, or longer than normal head hair called Hair Potters and not run afoul of a any trademarks held by any other products with a similar name... so long as it wasn't a gardening store (might have an issue with fair employment but that's not relevant to the question).
It's likely that "Techno Taco Tuedays" is sufficiently different in nature from Taco John's but similar enough to Lebron's attempt that it was denied. I am unfamiliar with what Techno Taco Tuesday is but, going out on a limb, for argument's sake if it's a web media promotion that releases Techno remixs from Mexico every Tuesday night or a weekly musical event where a DJ takes popular music from Mexico and gives them a techno remix... or said DJ goes by the stage name "DJ Taco"... Or maybe has blogs where he eats tacos to techno music every Tuesday... which Lebron's trademark attempt would be quite similar, but John's trademark is not violated.
Eitherway, it's not always the phrase in the trademark is not protected, but the meaning imparted into the phrase that is. I can say "Just Do It!" all I want... but if I slap the phrase onto shoes and try to sell them, I'll have words with the Nike attorneys. Trademarks typically protect the combination product's identity, but only when used in combination. A word or phrase itself is not unique... It's their association to the product's unique elements that is protected. I can make shoes if I want to... but I can't promote it with elements Nike trademarks.