Yeah, back then assembler was even more pervasive. It was the only way to write something publishable on 8-bit systems. Well, there were some action games (like C64 Beach Head), trivia and adventure games written in BASIC.

You spent a lot of time on 8-bitters getting code and asset size down, so that it'd even fit on the machine in the first place. Forget about luxuries like division and multiply, most advanced math those things could do was little more than adding (add, sub, and, or, xor) two 8 bit numbers together. Even shifts and rotates could only handle 1 bit left or right.

CPU clocks were measured in low single digit MHz. On top of that, 8 bitters were very inefficient — each instruction would take 2-8 clock cycles (6510) or 4-23 cycles (Z80).

On PAL C64 you have 19656 clock cycles per 50Hz screen frame minus 25 bad lines. So you could realistically expect to execute only 5-8k instructions. If you used all the frame time for just copying memory, you'd be able to transfer just about 2 kB. Just scrolling character RAM (ignoring color RAM) took half of the available raster time (yes, I know about VSP tricks, but it wasn't known in the eighties).

16-bit systems allowed some C, but most Amiga and Atari ST games were written in assembler. I'd guess same is true for 286 era, but not sure.