Why do different dictionaries seem to have different nuances in word definitions?

Language isn't math. A words meaning doesn't start from someone deciding on a meaning out of thin air and assigning a word to it that must always exactly and without exception be followed or things break.

Dictionary entries are -attempts- at capturing what a word means. There's no standard

All that said, some dictionaries are more respected than others. And separately, some websites are easier to use than others.

OED is the best English dictionary for reliable accurate nuances of words, but 1) it may be a bit of a fire hose, 2) it takes a bit of scholarly ambition to use and 3) is not immediately free on-line (but is often available for free through a local US or UK library.

Merriam-Webster is the next best (but is mostly just American English).

Most other online dictionaries are useful for language learners or casual users. They give passable definitions that will allow you to understand a newspaper or novel. Oxford Learners/Lexico/Collins/dictionary.com/vocabulary.com/etc/etc/etc. But don't think of them as legal documents or scientifically exact stipulations of usage. They're just trying.

You may have noticed that I have not mentioned Urban Dictionary or Wiktionary. UD is good for getting a vague idea about slang, but it is supplied by users who are not necessarily interested in explaining anything, and may not be invested in quality. Wiktionary is also crowd-sourced (by people who are interested), but is built up from scratch so there are a lot of gaps.

The best bet is to do what you just did, consult more than one dictionary and see what is common.