That suggestion has been put forward a number of times since the limit was put in place. One problem with that is that it is a backwards incompatible change so there need to be some signalling mechanism in place to ensure the rule change takes place at the same block height for every node. The logic would need to have been put in years before it activates.

A more longer term problem is the governance problems it entails. Large economic interest will want to adjust that value to their liking, so it should preferrably be a little more non-arbitrary.

So a more flexible approach is necessary, preferrably one that is backwards compatible for old nodes. Extension blocks, and a special form of extension blocks called segregated witness, can do exactly that. They have other problems, but most are pretty well understood by now, and most developers see segregated witness blocks as a way to more than double block size whilst minimizing risks.

(It also brought along the possibility to fix other long standing problems with the transaction format, so in the end several other things such as script versioning, uxto defragmentation and non-malleability was stuffed in there.)