First, a clarification:
I don't think there's no use for an IFV, or there's no use for its autocannon, or the (small) squad in an IFV is entirely ineffective. Instead, I argued that if it wasn't with us, we wouldn't introduce the IFV concept based on the state of military art and technology.
The IFV (infantry fighting vehicle / Schützenpanzer) benefits from a technological lock-in.
The standard example of a technological lock-in is the QWERTY/QWERTZ keyboard. Many millions of people have learned to type quickly on such keyboards, so other (supposedly better) keyboard layouts cannot have a commercial break-through any more.
It's similar with the IFV: Millions of people have been convinced by its concept and all armies with IFVs have an established pro-IFV lobby.
Those who would trade an IFV for an (H)APC would experience a loss in some squad capabilities*, and it's against human nature to like this no matter whether it's beneficial in the greater picture or not.
IFVs are also much preferred by the arms industry; as the integration of a turret and of MBT-like sensors and other electronics yields much more turnover and thus profit per vehicle than an (H)APC would ceteris paribus.
On the other hand, the in-service IFVs are mostly developments of the 60's or 70's, a generational change is necessary anyway. It's an opportune time for shedding the IFV that's on a gold-plated road to a dead end and to add a replacement to the vehicles fleet that strengthens the infantry arm to the proportion required for a good mechanised combined arms team.
*: It's at least in some armies common to consider vehicle, vehicle crew and dismount element as a single squad.