it's because when you burn a saturn game you can't burn on the protection code that sega puts on all their cd games. When you swap, the saturn is reading the code off of the original cd so it thinks that it is reading an offically licensed sega product because of that code.
i know sega just wanted to make it that way,jeeze as far as i knew this was the place to ask questions.i was only asking becouse maybe there is a way around it.and after some digging around on the internet,i found this guy on about it,and his idea is to either rip the contents of the saturn bios chip,modify the code then burn it back with something called an eprom burner i think it was called.or his other way as far as i can gather is to rip the saturn bios,modify it to remove the copy check then somehow burn it on the cdr game disk,therefore bypassing the saturn bios.also the saturn protection is burned onto commercial saturn games.the reason why copy protection doesent get burned is becouse,it doesent get read in the first place,becouse the copy protection is on,a part of the disk that most cd rom,cdr,cdrw drives do not or cannot access.anyway all this comes to nothing,becouse at the moment,no one is trying out these ideas.but if we get people talking about it,maybe some talented pc guys could maybe do it.which would be good for all.you answered my question,reluctently,as though it was a pain or chore to answer me.i wont bother asking you anything again.sorry to have troubled you.
Browse around old threads here, the Saturn copy protection scheme has been discussed several times.
Basically, you need special hardware to read the protection and you can't write it with a burner. Modifying the BIOS probably won't help either as the CD subsystem is isolated from the main CPUs and the software for that might be integrated with the SH1 processor (I might be wrong here, though).
Anyway, if you just want to play the games, get a modchip. They're cheap and easy to install.