that's probably because virtually all commercial DVDs are DVD-9 these days, rather than DVD-5.
DVD-9 is the code for a dual-layer DVD disk, which can hold up to 9.4GB of data.
DVD-5 is the code for single layer DVD disc, which is the most common one found in the consumer market as DVD±R.
So, if you're copying DVD-9's onto your hard drive using MacTheRipper, then trying to burn them directly onto a DVD-5 DVD±R, then it's not going to work - there simply isn't enough space.
DVD2One X will shrink the DVD-9 movie down so it fits on a single DVD-5 disc.
http://www.dvd2one.com/