Dumb questions re. file size

Excuse my dumb questions, but I’m trying to burn DVD’s for the very first time!

I’m basically trying to transfer family view films from an old Panasonic movie camera on to DVD. Using Nero Film Capture, I first used the DVD template, but had real problems with frames being dropped. I noted that the DVD template used 720x576 resolution, so tried the same size but this time using the MPEG-2 template (at ‘best’ quality). This time I didn’t drop any frames, and the file sizes were much smaller. Why are the file sizes much smaller with MPEG-2 than DVD?

Having now captured all of my film into MPEG-2 files, I now wanted to split one of the files into two, as the subject matter was different. I did this using Nero Vision, but couldn’t just save the new files but had to ‘export’ them. Is this normal? When I exported them, I again used 720x576, but the file sizes massively increased. Why? Also when I view the new files, the image is now far bigger than the original.

Probably dumb questions, but I’m very confused.

Surely the mpeg2 template uses a lower bitrate than the DVD one.
If the target file is much bigger, no compression were used…