Enshittification is coming:
Beginning in the next month, when users click Bitly links or QR Codes, they may see a preview page prior to being directed to the destination URL. The page includes information about the link destination and may include advertising.
They’re useful for printed media
“Find more info at bitly/event” instead of “find more info at facebook.com/unnecessarilylongurlthatnobodyisgoingtotype”
Or for a qr code where it needs to be small and somehow your URL is too long
But yes, relying on a third party company for something that needs to last a long time isn’t really smart. There are many books that have online content now inaccessible because they used a link shortener that’s dead or that doesn’t let you update the redirection without paying a ransom (need to pay $120/year to bitly if you need to change the redirection)