"Abusing users" in eshittification is fundamentally about violating expectations/norms, which is what Eternal September was about. Before "Eternal September", Usenet users came aboard in small waves and acclimatized to the local culture. This was the norm on Usenet. Once Usenet opened up, users joined so quickly that they could participate in the network with no shame without acclimatizing to the local culture. Likewise, when more ads appear or previously-free API surfaces begin costing users, older norms/expectations have been violated.