Maximum skill gem is only 40?

I am currently running lvl 40 shockwave totems. They scale great with dmg on level up, approximately 16-17% more damage each level. I have items that allows shockwave totems to reach lvl 43, but neither the damage or gem level increases, it is hard-limited to 40 (this is not the prismn of belief bug).

I believe the theoretical maximum level on shockwave totems are lvl 45, so i am missing out on 1.17^5 = 2.2 multiplier on my overall dps.

Why are gems capped at lvl 40 when its relatively easy to go beyond?

"

relatively easy to go beyond

Therefore, the developer can run full scale test of their service. I don't think they have to exclude shockwave totem from the process.

/off_topic
Lv.1~40 is like there are A~Z rows and 1~1000 column in a spread sheet by default. We don't really have to expand a sheet to its limit and fill those cells just because it's possible.
Edit
I mean, technically we can have "lv 1.000~lv.40.000" gems scaling in increments of 0.001. It has 39001 steps.