I have had the same experience a lot while selling on ebay.
On the other hand, I reached out to a seller on offerup about a machine that was listed over a month prior to see if it was still for sale (I am over 30 and rarely use these for sale sites). I then make an offer the next day after no response and was told that an offer was received the day after I inquired, it would have been nice to be told earlier that it was still for sale.
The bottom line is that you should always respond when selling something. I don't understand the lack of common decency of communication now.