They didn't make them because no one bought them the last time around. Hell, if you keep your eyes open you can still find figures from the 2009 film on various retailers clearance shelves.
But it wasn't the scale, it was the execution. Hasbro OWNS the 3 3/4" category.
Then again, I know collectors who were disappointed that Playmates didn't pick up where they left off with their 5" figures so scale may have played a small role in the overall performance of the line.
I still think the Playmates line would have performed better if they'd have simply released a complete bridge crew in the first wave. Releasing the modular bridge playset over two waves was a big enough risk.