Because the pension is only one part of it. It would be possible to increase benefits, including the state pension, if, for example, we had a system which reasonably taxed the extreme housing wealth which disproportionately sits with that demographic, but they won't vote for it, so that's where we are.
When baby boomers overwhelmingly vote for "crippling student debt for thee, triple-lock and tax breaks for me" my sympathy is limited.