My master's thesis is on a topic in this field (Privacy Preserving ML) and from my understanding HE and other techniques have very high overheads(~10^3) on inference tasks and thus aren't very commercially viable.
That's the reason for HEIR like optimization and parameter selection. It narrows the 10^3 - 10^6 penalty to 10x - 100x.
I'm glad people fund things that are only of interest to nerds but this will never be useful.