I don't know what regulations they operate under for this but I got a bunch too from other airlines and of course Frontier. Some are for as little as 7 minute changes. Must be some time slot rules they had to conform to. Sometimes I don't accept them per se, but then I get new confirmation emails with the changes. I really can't see how it matters and this is normal for Frontier anytime you buy a flight with more than 45 days to go