Sure there are not enough staking wallets, but there may be another reason for network not staking well too.
If you look on block 22101, you could see a strange picture:
http://cryptobe.com/block/f4d0e725f0192d6a09aa9440b636de71a37b22147a140e319dc4d84a6dcd891cIt looks like 9 inputs were consolidated into one single input after the staking! It means next time instead of 9 blocks those coins could generate just 1 block.
Even worse is on block 22100 (
http://cryptobe.com/block/54310354d8df0be1f957e03e4ad9a32fe9ed606d5a3488b356618314ad57c19d) - about 30 inputs were consolidated into one.
I am not sure why this happened, but if the wallet does it itself, then after some time there will be very few inputs to stake.
I have seen wallets dividing coins after the staking (that creates many small inputs, which could be inconvenient, but it definitely supports the network). For example CoinAid wallet does that. But here it looks we have the opposite, and this could be a problem.
These are just my observations and assumptions. They might be wrong, but if they are correct, then wallet code could need to be tweaked.