It is actually because it is nearly guaranteed to be collectible when it is attached to inelastic goods which are needed by everybody. On the other hand, raising things like estate tax and income tax increases the amount of legal tax dodging through trusts, municipal bonds and the like so it's unpredictable and difficult to collect. This dates back to a reversal of Andrew Mellon's prudent and lucrative tax policies by FDR and Morgenthau, who turned to gasoline and alcohol taxes to cover shortfalls caused by their extremely high progressive income tax rates, and since then high earners have gotten in the habit of tax avoidance regardless of current political and fiscal strategies, permanently entrenching the regressive taxes as necessary.
I'm not sure I buy that as a "because". I think it's more likely sales taxes are passed preferentially because income taxes are more often defeated in legislatures due to political opposition, not because of technocratic arguments about collectibility.
It would be interesting to have some numbers on collectibility, though. Both income taxes and sales taxes can be dodged (black-market purchases and out-of-state online purchases are two common ways of dodging sales taxes). There are a number of examples of states raising either one, and it'd be interesting if someone has extracted data on the results.
