Dathi pretty much hit it on the head here. Crossbows were good at piercing armor, but absolute shite at reloading speed. This was why longbows were also used at the same time. But by the time that the mechanics were practical to have relieable repeating crossbows, firearms had already been well established.See also
WI: Europe imports the repeating crossbow
MrNumbahOne
WI: Europe imports the repeating crossbow
MrNumbahOne
Romans invent the repeating crossbow?
Darkest
It's really a dead end. There's only so much energy you can store in a crossbow, and if that's split over multiple bolts, each of those is going to be very ineffective. And it will be mechanically complex, horrendously expensive and probably break down in battle conditions.