They search for weak spots, and your only city with 3 generals and 1 or 2 units fit perfectly in definiton of weak spot :)

got full stack seging my capital after some 8-10 turns (2 years)

On VH (camp map) only money I got was 2000 minai from romans for Aliance, trade rights and map info. Any other faction I asked (without aliance proposition) replied with "give us 1500 tribute for 5 turns" or sth like this. Maybe I'm just awful negotiator ...