Why does many sites (youtube is good example) generate string of random number and letter instead of using for example the row id?

usually its something likes this

bla?v=wli4l73Chc0

instead of like

bla?id=83934

Is it just to keep it short if you have many rows? Or is there other good things about this? Because i can imagine: bla?id=23934234234 dont look so nice

Thanks and cheers

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