Firstly its not what the cartridges cost to produce its what Nintendo charge the publishers. If Macronix charge Nintendo $2 for a 1GB cartridge and $6 for a 32GB cartridge that doesn't mean that is what the publishers pay, it could be $4 for a 1GB cart and $9 for a 32GB cartridge. We just don't have the figures but Nintendo will put a good cut on for themselves.
I'm sure many games will be cut down in size for Switch. Many games were cut down in size on Vita over ps3 versions even though the Vita has more memory than ps3. This is simply a factor of cartridge costs and limited flash memory storage. Portable vs home console issues really. So it shouldn't be surprising if Switch games get reduced in size over wii u. 20GB is almost all Switch flash memory if you don't expand it.
To a lesser extend there was the same issue with 360 vs PS3 due to the ps3's bluray disc and lack of hard drive on many 360 consoles. PS3 games were often larger than 360 games, better high fidelity audio tracks, more pre-rendered video often at higher resolutions and sometimes additional content and that was simply due to the dvd discs vs bluray discs.
I don't think publishers should be criticised for releasing smaller games on Switch its a portable system first and this should be expected.
