I don't know, I assume you are giving me a couple of clues? Most people don't actually shoot animals that are nervous from hunting by stalking in less than 50m and they are a way overpriced for something that has the range of a 36ftlb BB gun?
You have the answers - doubles are expensive, bolt actions are more accurate and with a scope your 375, 416 or 458 can do double duty on smaller game at longer ranges. And they are very much cheaper - A big bore Brno with a scope is going to cost 1,000 $ of £ to get up and running and shooting well. A double is going to be five times that.
There has been a renewed interest in double rifles over the last 10 / 15 years. For a professional hunter who is only going to shoot when things go wrong and you are dealing with something that is big, cross and wants to kill you and your clients, cost of a double is irrelevant. You need two quick shots, and then another two quick and then another two quick shots at close range. Where a double is used, you are in thick bush and visibility may only be measured in single digit metres. You can get two shots off with a double, but with a bolt action its going to be a single shot. Lions, buffalo and elephant can move very fast.
Cost of a fine double is in the labour required for all the hand fitting. Yes modern CNC machinery brings the cost down and there are now plenty of good over and under and side by side doubles for similar cost to higher end bolt actions. And if you want a cheap double rifle - get a Baikal - they work.
I now have a double 7x65R - with its bottom barrel, its accurate out 150 / 200 yards. Its top barrel shoots close enough to point of aim at 50 to 60 yards. I have it for shooting driven wild boar in Germany. I can put two shots into a running pig, and then quick reload for the next one. I could have got a left handed plastic stocked bolt action 30-06 or 9.3 for less than total cost I have spent on this, or I could have got a R93 or R8 for the same sort of money - either would have given me three or four quickish shots, but then slow to reload. I like the way a double handles, shooting is a hobby for me and I like using a fine gun.