Well nowhere in the page does the author mention any attempt to be authentic or using html written the same way ad in the 90's so I am wondering where does that negativity come and why?

It looks to me this service is proposing hosting like it is the 90's, not building a web page exactly like it is the 90's with just a wee bit of retro clues.

The whole site goes on about wanting to recreate the feelings of the 90s.

That's it, feeling.

The same way a Mazda Miata gave you the feeling of driving a british roadster of the 60's while having much more modern internals,comfort, reliability and fuel economy.

I've never felt comfort in a Miata haha

Interesting final point you bring up because all of those shortcomings are part of the experience, without them you’re experiencing something completely different. (As a classic car owner that’s not entirely a bad thing in the case of the MX-5).