Because even new devices have to be as cheap as possible? Looks like a kind of some tradeoff… It’s not only about ports and switches but also about cpu because users normally expect that device having gigabit ports is able to forward data at that speeds… But otherwise you are right even not everyone needs gigabits for home web browsing yet.
It is a “lite” product! And you will find that in practice such wireless links will not go anywhere near 100 Mbit/s full duplex, no matter
what the sales brochures tell you. WiFi specs (of all manufacturers) only refer to raw radio rates, not to net end-to-end throughput.
And THAT is what matters when considering the ethernet speed.
With “normal” N-type radios you will not be able to achieve 100 Mbps full duplex throughput.
With AC maybe, but probably not either.
So even with 100 Mbps ethernet, AC may be desirable.