For the same reason why volks don't get a t0 Faust, because there has to be a window of opportunity where clown cars must be effective, otherwise what's the point of a unit? Same is true for ostwinds and centaurs (in theory) are cheaper than p4s and Cromwells, there has to be some sort of reason why to build them when their counters (which are also generalist ai/at units) are soon arriving.
Back on topic, and that's even assuming that in live there is a huge window where the luchs is available and the Stuart and AEC arnt. I just don't see how a luchs which takes 115 fuel to get out (accounting for starting fuel) where as an AEC takes 75! I may be wearing some damn tinted glasses but how OKWs supposed "unbeatable" early game can get them 45 more fuel in under six minutes?
And that's assuming that AT guns and bazzoka blobs arnt a good deterant too.
As I said above such a drastic build time increase is unnecessary in my opinion and even if we disregard that due to my blatant fanboism, such a change is a poor solution to the problem, especially when allies are getting new early game buffs. A much better solution would be to increase its mp cost by 20 - 40, this does make it slower to come out but can be mitigated by good early gameplay or to give kubels a small 5 fuel cost.
OKW Volksgrens have no T0 faust because OKW has a cheap T0 AT-gun. They also have mines so saying that OKW cant counter clown cars is a bit weird.
AEC comes out faster than Luchs if everything else is equal. I never said Luchs comes out faster than AEC.
Centaurs and Ostwinds are effective at any stage of the game. They aren´t limited to some imaginary early mid-game window.
I think something almost anyone will agree on is that Luchs needs to be reworked in some way because playing against Luchs rush in every single 1on1 and most 2v2s is super annoying and boring.