I'm sorry, but mediocre music is not the result of the tools. A decent tunesmith will make all you haters (temporarily) "putting up with" the cheesiest synth sounds. Yes, even the synth sounds you detest so much.
I'm not saying that you will suddenly fall in love with ALL cheesy synth, but you will make an exception for well-crafted tunes.
While there certainly are "trends" in music (style-wise), I don't think we can condemn entire eras simply based on trends alone. Why? Because there will always be some totally great tunes that slavishly adhere to an era's trendy formulas (they are the "exemplar" tracks), plus you will have tunes that occasionally break the formula and redeem themselves with a few moments of originality/freshness. Sometimes you'll be lucky to stumble upon tunes that completely defied an era's conventions, but these are less common and often produce extreme reactions (love it or hate it, no middle-ground).
Please note, I am not discounting (or even denying) that particular trends/conventions exist (and evolve over time). I just think it is far too simplistic to blame lame music on hardware, cheesy synth sound libraries, etc.
To bring spenoza's point into my earlier formula, we have a very boring (but accurate) idea of why lame music is created:
(1) time
(2) money
(3) talent (or lake thereof)
(4) purpose of music (standalone vs. incidental vs. intentional muzak) (there are pros/cons with each approach)
(5) influence of conventions/norms/trends vs. willingness to flaunt conventions
(6) our (consumer's/fan's) expectations for RPG's to adhere to established conventions (see below).
(7) the commercial component (selling a game/critical response/customer's expectations) creates a tendency for companies to err on the side of conservatism. Conservatism produces lots of muzak.
TANGENT RANT
RPG's suffer from very strong conventions, unfortunately, and it is very rare for designers/companies to experiment with different musical genres/moods/song structures/arrangements/instruments/etc.
Not to start a war here, but I personally believe that many of the RPG soundtracks that are beloved by many people are extremely conventional (employing trendy, for the time, arrangements, instruments, song structure, etc.), but they are executed well and have just enough artistic flair to transcend being totally generic.
I am purposefully being antagonistic towards RPG's and their history of lame music, but everything I wrote can be applied beyond RPG's. It's more fun this way, though.