If you go bancrupt you don't have to repay loans either. And taking 20 loans costs you 75 admin (reduce inflation action) so it's not that big of a deal.
You also have to give up 5 years of the game every time you do it, also you can't be desinheriting heirs if you rely on bankruptcy, which means every point becomes more expensive, and mps are much more important than money (money can buy up to 60 mps per year through lvl 5 advisors, mps can increase income indefinetely by developing), also the stab raises, also you can't really do it before being a strong nation, and by that time you should have a good economy already. And of course selling crownland isn't mutually exclusive with taking loans.
I like selling crownland in the 15th century to get that initial economic push (coupled with deving up the capital for renaissance) in poor nations that need it, but obviously you can't rely on it if you hope to be close to 100% crownland by the time absolutism arrives.