Unless it's genetic, which is unlikely in this case, there should be other growth happening, regardless of routine. I can't say what's out-of-whack, but can tell you that I'd top it pretty quick, especially if you're in town. Topping it will/should force that side growth.
I have no clue why a bigger planter would make any difference when side growth usually appears on plants in 2" pots.
Good luck.
Fishy