They could, but they just show the timestamp of the block.

The “time since last block” is always relative to a specific node because not all nodes receive a new block at the same time.

It’s possible that your node receives a new block half a minute later than mempool.space or the other way around. Or a node can receive block x+1 before block x

This time problem is the reason why we have a blockchain. It’s not possible to say which order of events is the correct one when it comes to decentralized networks. It’s a extremely complex topic