To be brief, I agree with the comments by
Rando, Valgar and
icycalm.
Rando wrote that shoot'em ups are 'niche' = very true, they always have been. For instance there have never been more than 10 hardcore arcade shooter players in the London arcades over the last 20 years. 6 of them are still around. - That's VERY niche!
So...it doesn't surprise me one bit that Valgar wrote that no-one plays
Ketsui etc. in his arcade, even on freeplay

.
My findings have been
the same in Casino arcade:- Over the last year,
ill6 and I have installed 6 shooter PCBs and they only attract 'curiosity cash'.
In contrast, I helped arrange the purchase of
Tekken 5 Dark Resurrection for the London arcade VS Players and that 1 beat'em up has packed the arcade out every night since installation!
icycalm's comments about Japanese arcade players almost never talking to one another must be a culture issue. The London arcade players are sociable on the whole.
The overall Topic of 2Dshooter popularity in Japan as against the West can be partly apportioned to the fact that western developers want to push and sell 'their own stuff' ie. pseudo 3D Grand Theft Autos etc...
They have been successful at brainwashing the general public in that respect.
Regs, DEL