Just out of curiosity, do any of you guys know why there is this trend?
A quick and unscientific google search doesn't really turn up a decent answer. One article mentioned Obamacare (though they did refer to it as the "affordable health care act."), and how it apparently gives incentives to employers who keep their number of full time employees under 50. My current employer seems to anecdotaly confirm this. They recently cut all part time worker hours, so that no part time employees are now ever scheduled more than 29 hours per week, and are not allowed to pick up any shifts that might put them over this threshold. They don't deny that it's because if employees average more than 29 hours, they are required to receive benefits which would cut in to the company's bottom line. My point of view on it is very cynical, but they are not the only employer who is doing this.
My personal thoughts are based only on speculation. I admit that my research in to this is minimal at best. But it seems that large employers want to essentially reinstate slave labor. They pay enough to make sure their slaves have room and board, but keeping them as part time helps make sure that the slaves will be ready to work whenever the master calls (because they need the money), and the master never has to do anything more than the bare minimum required by law. The fact that Obamacare is giving employers incentives to keep employees part time, and to prevent them from getting benefits, is just a convenient coincidence that employers are using as an excuse to justify their actions.
On a side note, Streets, have a +1 for leading a conversation with an open ended question rather than a blunt force opinionated statement. You're doing it right.