Aren't 2 and 3 already on the PS4 and Xbone anyway? Sticking them into one collection is easy there since the games already exist on those platforms. Porting them to Switch would be a lot of work.
I wouldn't say this is quite the same as the Mass Effect shenanigans back on Wii U, especially since this is the first game and not the third. Plus, ME 3 launched at $60 which was the same price of the trilogy. The Dark Souls Trilogy is going to launch at $80 while the Switch Dark Souls 1 is $40. I don't think it's a big deal in this case.