It's pointless busywork designed to scale according to how many other people are doing the same pointless busywork.
It is not pointless, it serves to process the transactions in the bitcoin network so that everybody can say with certainty which order transactions were posted so anybody can verify their own transactions.
If you do not see why we need mining, it might be helpful to read the original bitcoin whitepaper by Satoshi.
You might want to actually read it yourself; yes the round winner will process the aggregated transactions but the actual hashing is solving nothing in particular, though a scaling nothing in particular.
The whole network could be run on a NES if it was only about the transactions.