why did they made two kinds of tv pal and ntsc?

Question

why couldn't they use one kind?

Answer 1

Rhetorical question. Who is this "they" that you think exists.

NTSC was developed in the US based on late 1930's technology. The US has a 60 HZ power grid.

PAL was developed in the 1960's in Europe where there is a 50 HZ power grid.

Given the technology that was available when PAL was developed, it was not practical to adopt the 30 fps of NTSC in Europe, they went with 25 fps.

Since the designers of PAL were starting over with improved technology (rather than adding color as a patch like NTSC had to do), they could also use a more advance design in their color circuitry to make it more stable.