I'd certainly take issue with you here, though I understand your basic point. (Perhaps my use of the term "nice" was misguided and insufficiently explained).
Well, the issue of something's being 'nice' and something's being written with the aim of people liking it are two different things, so worth looking at separately.
I don't believe that writing/constructing art because you want people to like it will automatically by definition lead to a lack of creativity or ideal. If this were so, how do we explain Mozart, among countless other artists?
Well, Mozart comes at the very end of an era where the whole idea of artistic subjectivity was changing radically. Crudely put (you probably know this, or at least know this model even if not necessarily accepting it), the shift was between the composer as a servant, essentially writing to order what was required of them by their feudal patrons, thus to some extent putting their own will, desires, ideals to one side, and the Beethovenian notion of the composer following their own ideals, unbeholden to anyone else (of course this situation was made much less unequivocal by the rather glaring fact that the composer still had to sell their works on the open market, thus being beholden in that respect). Now, there are plenty of people who don't think this latter ideal was a positive move forward (much of Richard Taruskin's recent Oxford History is devoted to attacking this); others, including myself, see it as a fundamental step forward, but also one that is in various ways anticipated in much earlier music, going back a long way (as Taruskin also believes, but he valorises that in an opposite manner). The Beethovenian model of subjectivity and the creative process never really firmly established itself in various places, including Russia and the Soviet Union, and certainly in Britain (and that can be seen in much of the relatively impersonal music that generally emanates from British composers of all persuasions). It's all about whether one attempts to satisfy pre-ordained expectations, or follows one's own will to some extent independent of these.
Nor do I accept the logical corollary of your argument, viz that "entertainment" is "nice". I have rarely watched the popular soaps, but have done so in the past often enough to know that they are far from "nice", (in the usual broad sense) even though millions seem to find them entertaining.
I don't conflate 'nice' and 'entertaining'. Plenty of not-very-entertaining culture is 'nice', and plenty of 'entertaining' stuff can be nasty as well.
I'd alos be interested to know which precisely are the "other ideals" that, for you, are more important than beauty in the music you admire. I suppose I am asking "what greater satisfaction, motivation and worth could there be for any artist than creating beautiful art that is loved and appreciated by many?"
Well, I'd say something like 'truth' (without necessarily taking the position either that beauty and truth are identical, or mutually exclusive - but I don't really have so much time for the whole concept of 'beauty' anyhow). Art can say something meaningful and powerful, without it being either entertaining, nice, or loveable. But it can be important nonetheless. Don't really want to get embroiled in lots of detail on this in this thread, though.
As to Bach - it's that term "nice" again - and I agree that it is often inappropriate. But all that he wrote, nice or more than nice, is certainly eminently satisfying to hear and has its own musical beauty. Which is why he wrote it. Could there be any living composer who would not wish to be able to write as Bach did?
There are few higher ideals that a composer could aspire to (and in many ways Bach, certainly an idealist, anticipated a Beethovenian model of subjectivity). But there's a lot of music of today that is a step backwards rather than forwards from Bach. Bach himself was a unique individual, whose musical language and preoccupations were the product of a particular relationship to a particular historical era. Today, to write like Bach is not necessarily to attempt literally to sound like him in a detailed sense.