Dual-layer DVDs didn’t come out until later. Long movies on single-layer (or those whose producers were too lazy to optimize compression or use dual-layer) DVD had to be flipped mid-movie as well.
Besides unlike the one hour max on an LD, a 120 minute movie will fit on a single side single layer, so most early movie releases would fit on a single side single layer (the quality did suffer).
More commonly in the early days the dual side was to provide a pan and scan and letterbox option or extras.
There are so called “flippers”, but they weren’t that common.
An LD is 1 hour max so you are almost always flipping for any feature length.
DVD-10 single layer, double side
DVD-9 dual layer, single side
DVD-18 dual layer, double side
With the dual layer discs, the first layer had to be larger than the second layer. There was a slight pause when switching layers, and care was taken to place the layer break at a spot to hide that pause as much as possible. At least on the discs where the author took pride in work unlike the YT decisions on when/where to place ads. Although, I've seen some really poorly placed layer breaks too.