Fighters taking fights on short notice is more like a struggling actor taking a part in a **** film, because the actor needs the money and opportunity.
Early in his career Hopkins took a televised fight as a late sub only a couple of hours before the fight. Pulled it off too with from memory a second round KO.
Opportunity. If you're not well known and are offered a short notice fight with a well-known fighter you're going to take it for the opportunity or the money.