On the other hand: transaction times are pretty fast and fees are usually pretty low, so it is perfectly usable.
Perfectly usable for what? Is anyone using it for said purpose?
Im afraid nobody is using any altcoin for anything that isn't pumping and then dumping it for more bitcoin.
Ripple is a total shitcoin, it's pointless if you care about anything that isn't moving money fast from A to B without the underlying details. Any shitcoin can do this. Dogecoin can do this, any of the bitcoin forks can do this, this is not the point and this is not why bitcoin is valuable (only a part, but not everything).
So the answer is obvious: speculation. Ripple is pumped by X Y or Z big company = speculation starts and we have these peaks on the price, that is all.