From my experience, either an app reaches momentum and the author wants to monetize it or it was last updated 4 years ago.

Non-monetized good apps are few and far between. One of which is actually related, by thai-language.com: https://apps.apple.com/us/app/thai-english-dictionary-tl/id7...

It's clean, it has whole sentences mixed in the vocabulary, it links phrases parts to their sub-definitions, and lets you paste a whole sentence at once, defining word by word.

One of my favorite apps. Updated 5 months ago.