[ricardolopes]

Changing consensus rules requires coordinating a fork. This requires coordinating developers, miners and node operators. That may fly in pseudo decentralised chains where the community accepts whatever the leader says so, and even so, at high risk. In bitcoin, for instance, where there is no leader, this would never be a viable scenario.

Soft forks don't force you to download and run new clients just to be able to use the network, which is an important difference. You can use your existing client, you just don't have the new features and don't run validations on them.

The greatest risk on soft forks is that chain split you mention. That's why any reasonable soft fork deployment requires a long time window with a large majority of hashrate signaling support (like 95%).

[DennisP]

Changing a PoS checkpoint would also require coordinating a fork. Even if a dev team were forced to make the change, they couldn't make everyone go along with it.