During the eighties I would imagine that springers out sold PCP by a lot.
Most springers were still relatively basic and crude, and so could really do with improving.
The custom houses capitalised on this especially when the HW80 and 77 came along and they could develop them into very consistent and accurate rifles.
Now we have an off the shelf TX that shoots as good as most tricked up 77s. To improve the TX will cost a lot fortune for very little gain.
Couple that with now very affordable PCPs which are easier to shoot than the best tricked 80/77 or even TX.
There is no real need for the Venom Lazaglided re stocked springer probably costing £2k or more. Yes they will be the odd person who would pay for this but so few that the business model would not get off the ground.
You could argue that we are spoilt now. We can mostly afford the "dreamt" or rifles of yester year if we can find them for nostalgic reasons and have the best the manufacturers have to offer to shoot efficiently when we want. There is still a lot of old or new crap out there to buy, strip and experiment on too, so the fun tinkering is still there. Best of both worlds, maybe?

Different world too, think we wanted 77/80 on steroids and tried to make it ourselves as we couldn't afford one.
Think like this, HW100 + scope+ silencer+bag+7L Bottle etc. Then think the kids of today spend £1-1.5k on iPhone.