It's because they were plastered on Frostwire and Limewire when those were big p2p apps for downloading music. Infected Mushroom was the most abundant and first to be seen when people were looking in that direction. I've noticed their popularity spike too and it seems to have a nice corrolation with people getting high for the first time and looking for trippy new music mid 2000s. Shpongle and IM seem to be in every head's repertoire even if they don't know any other artists in psytrance, psy styles of ambient, dub and whatever. Its always Shpongle and Infected Mushroom for some reason, and the reason has a great deal to do with the internet, not touring. Whats easiest to come across on the internet is what is popular I guess?