Great question – unfortunately, we looked into this during our last round of firmware updates and we were told that there isn’t enough room on the chip to add it.
Yes, it’s been a headache lol. This is why in 2.31, we added the ability to join the bulb non-securely vs in S0 mode as ST only allowed either S2 or non-secure.
I wish I had better news and please know we tried to get S2 on the bulbs, but ran into a memory issue. The other avenue we tried (and failed) was to get the bulbs in 700 Series, but the issue we ran into there is that the manufacturer was being told by Silicon Labs that they needed to buy 1M 700 Series chips (these are special to bulbs and not the same as what’s found in every other product – something about heat dissipation and California Title 24). We sell maybe 20-30k of these bulbs a year, so we’re far from 1 million 
As a side note, I’ve switched over to everything non-secure and it’s lightning fast. I realize it can be a risk from a security side, but I don’t anticipate anyone standing at my front door with a scanner and controlling my bulbs. You never know I guess!