I don't understand it

So I have two online friends, we're not super close, so I don't expect any deep, constant messaging, but one thing really confuses me. One of them tends to text me every few weeks, sends me some videos, memes or sometimes even a wall of text and when I respond they just disappear for another few weeks without any response to my message. Then rinse and repeat. Another friend is kinda same, but he texts me like every two days. I respond to his messages, but when I send something I often don't get any response or reaction. I wonder why do they even text me when they don't want to talk? I know they're not obliged to text me, but why waste your time on finding memes or writing a whole paragraph of random things and then disappear? Can someone explain it, because my autistic brain can't comprehend it?