Some people are just greedy. I've seen people in my previous guilds do it in guild groups before, and pugs do it all the time. I've already emphasised that solo shinies should be left as they were because a) solo shinies were never an issue that needed 'fixing', and b) I recognise that some people couldn't care less about this particular issue, but it will affect how much time I spend playing the game, and whether I play at all once I get bored of regular content.
Heroic rare shinies are a different matter entirely, and I've never made a single plat profit from selling them. Making them no-trade or not makes no difference to me, although I'd prefer if they were no-trade so I would have a fair chance of completing collections. They've always been a contentious issue and it's good to see the devs address it, but there was no good reason to do the same to solo shinies, at least no good reason I can see from a players perspective anyway.