According to LinkedIn’s Homepage:
Over 120 million professionals use LinkedIn to exchange information, ideas and opportunities
So, we have a lot a professionals on LinkedIn. I assume that most of them would like to send a formal invitation to somebody when they want to add them to their “professional’ network.
Then why does the default invitation text use informal English?
Even though I customize it a little bit, I do not like to change the I’d into I would every time.