The only explanation that makes since is an injury. It would explain why he hasn't publicly addressed the issue and why he's still said pre-fight the last couple of fights that he's going back to his kicking game - only to not throw any kicks in the fight.
Whether it be a past injury to his shin/foot or maybe a knee/hip issue, it makes since to not publicly speak about it because why give your opponents more information than you have to. Much like a wrestler saying pre-fight that they're looking for the KO and are going to stand and bang, only to shoot for the TD within the first 30 seconds.
Kicking Aldo was the best Aldo. Aldo at his best is the FW GOAT.
Hopefully he can go back to at least throwing some kicks. Maybe not like in the old days, but at least enough to have a more diverse attack than his current straight up boxing approach.