A bunch of factors have converged here. Economics: the smaller the recording unit and performing unit, the greater the chance of surviving financially in current adverse conditions. Digital technology: the availability of cheap facilitation software (digital audio workstations etc) that encourages an artist to play all the parts and that allow for defective or uninspired performances to be corrected or jazzed up using editing, tweaking, filtering, etc. And the internet: while that comes into play more in terms of distribution (the artist-as-label phenomenon) it arguably fosters a non-interdependent mindset, so that it's literally do-it-yourself all the way through the process, as opposed to do-it-ourselves.
* Of course not every "interpersonal" and "interdependent" musical situation generates this precious spark. Most bands won't get close. Increasingly, these days I suspect, it's not even a goal; they're not aware it is absent. At the same time, the solo artist + machines can create something akin to vibe: a sort of heightened ersatz that at once surpasses and falls short of what can be done by live musicians together. Other producer-as-artists achieve vibe by a kind of vampiric siphoning. Effectively they groove with ghosts, commune with the absent presences of rhythmic others from remote times and places: vibes laid down in real-time, real-space sessions long ago, then engraved into vinyl, where they lay dormant until sampled and reactivated. Ace producers like Vibert or Dilla are seance masters, leaders of imaginary superbands recruited from the archive. The proof of this dependency on the analogue past is that samplers rarely sample from sample-based music, or indeed from programmed music. Generally they turn to hand-played music, the richest deposits of which are to found in the Seventies, when the peaks of analogue recording and of small-band groove-oriented music coincided.