My bamboo's not putting out many leaves

Some bamboos tend to flower and then die afterwards, some live on, but others just die. The few that keep appearing are probably pieces hanging on.
The shock of being split may of encouraged it to flower as it probably made it 'think' it was going to die and nature means it has to produce the next generation.
I find that bamboos don't really like to much root disturbance and very quickly deteriorate, almost with in days if division means major damage to roots.

i have a dead bamboo that i left in as its black stems and rusty red spent flowers still look pretty. so your bamboo might be just sulking, but depending on the species it may have died.
welcome to GoY too.

If it flowered last year, it's on the way out. It's the one plant you don't want flowers on - it usually gives up the ghost afterwards.