Are you referring to higher rates on a loan, or line of credit, if you are single?
If so, that may have more to do with financial stability - two earners are always a better bet for a loan provider than a single earner. So, a single person is a higher risk factor. That's not really "discrimination". The debt to income ratio used to factor rates will be different if you don't also have a spouse earning income. Therefor loan rates will be higher if you are single.
Then there's recovery if there is a default. If you are married and default on the loan/credit, the bank can go after you and your spouse. Which increases possible recovery rates. If it's just you, recovery would be more difficult, or impossible.
This is the same thing as having an excellent credit score or a poor credit score. You'll pay more if you have a low credit score because you are a higher risk. That's not discrimination.
In short, I would suspect the difference you are seeing, without detailed descriptions, are more about the risk factors lenders see between single and married individuals. It's not about marital status as much as it's about stability and defaulting.