I find most written-by-rote romance stories complete drivel. Yet they're generally hugely popular. I accept they're not my cup of tea and move on. Equally, I realise my British, slice-of-life, few HEA stories are only of interest to a comparatively small proportion of the GA readership. Different interests, different experiences.
As to quality... Yes, it varies. Bear in mind though, the site is free to access and writers do not get paid in any form. Those writers who see writing as a craft that needs to worked at, will do so. Writers at GA are encouraged to use beta-readers and editors but if they actively decide not to, that's their choice. There is however a grey area as well when newer writers may struggle to find the editorial help they'd wish for. Likes, recommendations, and comments sometimes have little to do with writing quality. In that case, it's easy to see why the writer might feel there's little pressure to improve.
I, for one, encourage respectful, constructive criticism. I've learnt a lot that way. But those words 'respectful' and 'constructive' are important. Also, I've learnt never to assume all authors welcome criticism - openly or in private. Stories here are not being critiqued prior to commercial publication. If an author over time gives little impression of improvement or expanding their creative horizons, it's usually a safe bet they will not respond favourably to criticism, however couched.