As further suggestive evidence of this, watch the correlation between donors/friends of those same old white guys entering the MJ business, and the rapid "evolution" of the willingness to switch stances on legality.
You can even evaluate this without malice: Some say MJ is dangerous, and some say it's great. The status quo is that it is banned. Changing that creates the risk that it is bad and the change will be blamed on you, but legalizing will not bring you much glory, so you support the status quo until you have sufficient incentive (most likely $$$, but a strong push from the public instead of "meh" would also count).
That said, I find a mix of opportunism and greed to be the most likely explanation.
You can even evaluate this without malice: Some say MJ is dangerous, and some say it's great. The status quo is that it is banned. Changing that creates the risk that it is bad and the change will be blamed on you, but legalizing will not bring you much glory, so you support the status quo until you have sufficient incentive (most likely $$$, but a strong push from the public instead of "meh" would also count).
That said, I find a mix of opportunism and greed to be the most likely explanation.