Dave O - You're so right about indiscriminate use of over-the-top compliments.
I won't praise something that I didn't think was praiseworthy. And I'll usually wait awhile before delivering a compliment - that way it isn't as easily mistaken for mere auto-complementing.
Its not really kind to tell someone they are marvellous when in fact they aren't. It can end up making them put themselves in a situation where they end up looking foolish.

Back to the thread topic. Sounds like maybe a mix of jealousy and not wanting the existing dynamics of the session/singaround to change. Maybe if you improve too much you risk making the non-improvers uncomfortably aware that they have stalled?

I hope you find a more congenial bunch - but in any case - full marks for being one of those that can and does improve over time. Onwards & upwards & all that....