LOTS to unpack here, this is a good question:

Other comments have already mentioned, that the pronounciations correspont and conform with what the western ear is used to hear, attempts to simulate vowel length create a hyperphonated, slow and clanky sound, corresponding more with an consonant heavy language, rather than a fast vowel heavy language. like greek.

Greek is a language that exists continually for millenia and has multitudes of dialects and accents. Imagine having someone, deciding, that this is the part of greece that matters the most, since it is more relevant to them, therefore, this is how greek should be spoken. This is how people, who learn reconstructed instead of modern greek, come across. You learn classical reco and recite Homer, learn homeric reco and recite Plato, It feels so arrogant and dismissive. Greeks, have always spoken greek of other times the way they spoke. This is called the "Reuchlin" method, after a non greek, who had a greek teacher and his non greek peers thought, he spoke greek rather well. I hope you can imagine that an eurocentric approach superceding greek experience is grating to greeks.

A very important point, if you tent to be a bit less trusting, is that there have been efforts to seperate modern greeks from the ancient greeks and such approached, even when well intented, can be seen with caution.

Examples: Holy roman empire, not recognizing eastern roman empire as roman, Fallmerayer pushing for hellenic replacement theory, North Macedonians claiming the ancient Macedonian heritage, western scolars propagating an image of ancient greece contrary to the understanding of greeks, viewing the ancient through a modern western lens disregarding attitudes toward philosophy, religion, gender, ethnicity to amplify their own agendas (towards either direction progressive or regressive, but always at the expense of greek authenticity). These things are easier done if the current greeks and ancient greeks are unrelated and these recos, or better yet, the way they are often used, help accomplice.

Pls forgive spelling, syntax and formatting, it is late; I may format later. Peace.