Assuming everyone who is playing a 1e ruleset would be playing a 5e ruleset if 1e was unavailable, yes.
That has nothing to do with it.
By
definition, the mere existence of a competing product that sells eats into the profits of any other product in the same market. That substitute could be getting 20% or 0.002% of the market, but that is money that's not going to the front runner.
And if the competing product is produced
in-house, that means that you're not only taking some potential sales away from your lead product (including some would-be new gamers), you're diverting production resources away from that lead product to produce the other one. IOW, cannibalism.
The ONLY reason a company produces multiple similar product is to capture buyers who would or could not ordinarily buy the lead product. In those cases, they are hoping to "grow the pie" by making consumers of non-consumers. With cars, this is done by having entry-level, mid-level, luxury, sport, off-road and other vehicles to appeal to persons in different economic strata, with different needs.
While on the surface, it would seem that this is exactly what we're talking about with the various RPG editions, that perception would be erroneous. Here, the each version of D&D is a complete game that would cost about the same to produce and purchase, but with differing design criteria...all with essentially the same name. They're more akin to differing trim lines within a vehicle than distinct vehicles within a product line.