Linkedin has not improved its problems with spam or content quality since Microsoft took over.
Not unreliable enough to be a problem though, and Actions seems to be a decent experience for plenty of people.
The simple fact with GitHub is that it is _the_ primary place to go looking for, or post your, open source code, and it is the go-to platform for the majority of companies looking for a solution to source code hosting.
Your comment about LinkedIn is true, but where is the nearest competition in its' space?