Jazz was ensemble based, and both improvised soloing and extemporanteous arrangement are a central part of performance. Twelve bar blues structure lends itself to a lot more possibilities than the sixteen bar structure, and is much easier to work with from that point of view.

If you know the conventions, you can take a single four count phrase and turn it into a great performance. On the other hand, if you and your crew are so inclined, you can fit 20 or 30 different ideas into that same space. That's a significant part of the reason jazz musicians adopted blues, though certainly not the only one.