Each bomblet inside the shells can be dropped by a drone. Ukrain is low on that type of munition as well.

Russia's mined the fuck out of the whole east and south of the country. Not just land mines, but little petal mines and crap all over the place. UXO/mine disposal is already going to take decades. Western Europe still explodes a handful of people with UXO leftover from WW1 and 2, but it was still worth supporting them with weapons to win those wars.

Ukraine likely intends to crack open the cluster bombs and use the 80 or so individual munitions inside for dropping from drones. These weapons are basically an 80-for-1 deal the US has no use for, and the west can't produce mutions fast enough to give or sell to Ukraine.

Because

1. Better a mined countryside than losing the war and
2. The countryside is already full of mines and stuff anyway.

As to other munitions: First of all those aren't exactly plentiful, secondly you'd also have to have the necessary hardware to have a similar effect on the battlefield. You can hook up a couple of PzH 2000, say, seven, put ordinary rounds in their barrels and tell them to all shoot say 10 rounds a particular area all 70 impacting at the same time (so that noone can take cover), or you can use one cluster round with a couple of duds in it. Ukraine doesn't just have a couple of PzH 2000s standing idly around just waiting for an opportunity to imitate a much cheaper cluster round.