Yes, but 1 MB is what most of the nodes accepted. It is mainly about backward-compatibility. If you would create such a soft-fork where blocks would have 1 GB, then it could be activated. Previous block sizes could be changed in a hard-fork way, because the network was small enough to do it easily. But as the network grows, it is harder and harder to do some hard-fork, because if developers can change things in a backward-incompatible way, then they can potentially change everything. On the other hand, soft-forks are unstoppable: https://www.truthcoin.info/blog/against-the-hard-fork/