;D :-[ :D
I agree with the last two responses and I can offer a perhaps dated but practical reason. Eventually you will probably find that a good night's sleep is important too and zipped together is FAR more restrictive in mated bags than a twin bed. I also believe that mate-able bags require a left and a right zip which is fine until one of you realizes that the wind baffle, or whatever it's called, covers the zipper on one and lets a whole lot of cold air in the other.

The crux of the biscuit IS the apostrophe ...

If you could both be happy in the same twin bed for the rest of your lives....