How net earners got their incomming channels?
Merchants get channels from customers who want to transact with them. This isn't something that needs to be specified; if someone wants to transact with you over LN, they can open a channel with you. This is how many transactions currently happen over LN - the customer opens a LN channel with the receiver. Furthermore, autopilot modes like the one used by LND will automatically open and close channels to various nodes so nodes that accept incoming channels will likely have connections from others where autopilot connected to it.