It also seems to add a "double jeopardy" element for the defendant,
even if the second jeopardy is just reputational damage and having to
pay money rather than jail time.
It doesn't. Double jeopardy only applies to two criminal prosecutions for the same conduct by the same sovereign. Civil lawsuits don't constitute double jeopardy.
So my question is, why don't victims do this all the time? Obviously
we can't look into the minds of every victim to understand the
reasons, but are there other challenges that make this impractical
despite it looking like a fairly obvious option available to them to
get restitution / justice?
First Restitution is routinely awarded as part of the sentence following a criminal conviction.
Restitution doesn't compensate everything that a civil judgment does. For example, it doesn't cover non-economic damages for pain and suffering or some more remote economic losses. But often, it covers the core economic losses from a crime.
Second The vast majority of convicted criminals are indigent and judgment proof or can only pay a little in excess of restitution.
Even an ability to pay restitution is rare:
Judges ordered 15 percent of federal offenders to pay restitution.
Offenses for which courts ordered restitution most often were fraud,
embezzlement, arson, auto theft, tax-related crimes, robbery, burglary
and larceny. Thirty percent of offenders convicted of murder were
ordered to compensate victims. The amount of restitution ordered
between 2014 and 2016 totaled $33.9 billion.
Between 2014 and 2016, U.S. Attorney’s Offices collected a total of
$2.95 billion. Half of that came from debts imposed between fiscal
years 1988 and 2014.
As of the end of fiscal year 2016, $110 billion in restitution debt
was outstanding. The federal government has deemed $100 billion of
that to be “uncollectible” based on the offender’s ability to pay.
Almost all — 95 percent — of offenders ordered to pay restitution received a waiver allowing them to forgo payment because they had no
ability to pay.
State offenders have less of an ability to pay restitution, on average, than federal ones, who are often white collar criminals or immigration offenders.
All criminal defendants with public defenders are by definition indigent. And according to the U.S. Department of Justice:
approximately 66% of felony Federal defendants and 82% of felony
defendants in large State courts were represented by public defenders.
Going to jail or prison deprives criminal defendants of a meaningful income while incarcerated and dramatically reduces their ability to earn income when they are released, again reducing their ability to pay a civil judgment.
Even when a defendant does have assets and some actual ability to pay, those assets may be protected from civil lawsuit judgments, for example, by a homestead exemption for an owned personal residence, or an exemption from creditors for pensions and IRAs. Also assets of a criminal defendant that aren't exempt from creditors are often seized by creditors of the criminal defendant due to inability to pay monthly payments during a criminal prosecution due to loss of income and employment, or collapse of a self-employed business, or use of available funds to pay a private criminal defense lawyer.
Third Lawyers won't file a civil suit against a criminal defendant, even knowing that liability is basically automatic and effortless in the case of a criminal conviction where all appeals have been exhausted, unless there is a realistic possibility of recovering enough from the defendant in the civil suit beyond any restitution award to justify the legal work involved within a reasonable time.
Fourth If a criminal defendant is acquitted at trial or the prosecutor declines to press charges, while this doesn't legally prevent a victim from bringing a civil lawsuit, as the O.J. Simpson case illustrated, it make it much less attractive for a lawyer in a civil case to take on and the risk that there will be no judgment or favorable settlement reached is great. It will probably be expensive to prove the case and the case will be hard fought.
Fifth The statute of limitations for a civil lawsuit in tort for damages associated with a crime often runs before the criminal proceeding is concluded if there is not a plea bargain, this makes the legal work in the civil lawsuit more expensive and often crime victims don't think about the possibility of a civil suit until the dust has settled in the criminal case and they realize that the restitution award received does not fully compensate them for their losses.
Keep in mind that crime victims usually don't hire lawyers because the prosecution is handled by state and local government paid lawyers, but victims aren't the clients of prosecutors and prosecutors usually don't advise victims on the possibility of bringing a civil lawsuit.