I think that's a bad objection. It's idealistic in the worst way, it's making "Perfect [...] the enemy of the good". Plus, there are significant practical advantages to a fixed-length addressing scheme, and any fixed-length going to have a maximum. So, under the constraint of fixed-length addressing "big enough" is all we have.

128 bits really is quite hard to fill up, we'll have to worry about a lot of very different things before the run out of addresses. Like speed-of-light latency vs. TCP (and possibly TLS session) timers for interplanetary connections.