> If it was the most popular then why has it fell to the way side then ? Why wasn't it
> not improve and evolved also ?
because none of the devs with any talent actually used it because it is/was a major inconvenience that gets in way of development, in addition, it is Windows specific and an awful lot of devs aren't on Windows.
most devs will recommend something that actually *works* for the full featureset of MAME like QMC2 and if any real work was done for MAMEUI it would end up turning into something like that anyway, as it stands somebody else has already done the work for us by creating QMC2.
the reason MAME has always moved forward, and is still going is because it's built more around the needs of the developers - rapid development, rapid driver prototyping, submit quick+early and improve methodologies, easy to add new features etc. not the 'popularity' of any given system or feature. MAMEUI really does nothing but slow development down so it's unsurprising the main devs have no interest in maintaining it.