It's not like your need a lot of text. Do you really think that producing 10k different messages is "expensive" for an intelligence group? (Not that you need to write that many with some templates and randomisation)

Yes, lots of people heard about bots and use the accusation incorrectly. But in many cases actual sockpuppets are easy to spot. There's lots of accounts used only for propaganda for example and switch from Chinese-supporting messages when there's something happening in China to Russia supporting content following some news, to Trump supporting the next month before elections. They don't even bother deleting old messages, because most people don't check / doesn't care.