Assuming that they are using a defined amount of money, as if to say there is a single pot used for all things, and any money spent must have been taken from that pot. What makes this notion a misconception is that CDPR has publishers. Here's a quick example of what I mean:
Publisher has 500,000,000 to spend on games (total for the year)
CDPR gets 150,000,000 to spend on Witcher 3
350,000,000 is left which could go to anything, CDPR could convince the publisher that a remake will be profitable and thus get 25,000,000 for remake
There is still 325,000,000 left (not purely for CDPR of course, it's there for any company that can convince them to publish)
If the remake is profitable, both CDPR and the publisher have even more money to spend on games, this is why we see things like the Halo Master Chief collection, because remakes are a relatively cheap way to profit.
That said, I don't believe a full remake is necessary, just some updates (at least for The Witcher 2). I'm just saying you shouldn't look at everything that isn't important to you as if it's going to impact what is important to you. Too often I see people take a stand against ideas that will likely not impact them because they fear it somehow will impact them. If we were talking about making an entire game from scratch with a big budget you guys would be completely correct, but a remake using an existing engine would not be large enough to impact development of new games.