I see this comment on GitHub, and I'm guessing it's probably spot on:
I don't see IMDb "fixing" this issue anytime soon to be honest; they probably caught on that a metric shitload of users are scraping their IMDb watchlists from Sonarr & Radarr, generating heaps of traffic that IMDb has to pay for.
That sucks, but it's probably not high on Amazon's priority list of API issues to fix.