May - the season of giving (spending)?

Is there something I don't know about the month of May? I have two personal credit cards, and both of them bumped my credit limit by ~25% in the last couple weeks. I'm not complaining*, but something seems a little fishy.

Are they trying to coax me out of my post-Christmas cheap phase**? Are they that eager to pay for our plastic money infrastructure while I give them exactly $0 for their efforts? Hell, my Citi card pays me. Do they make a significant amount from selling my name to third party "marketing partners"? Enough to take on the extra cost (of a higher credit limit) in order to retain me as a cardholder?

Moral of the story: The credit industry makes no sense to me, but at least this time it makes no sense in my favor.
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*Actually, I might complain a little. I really wish I could transfer the (higher) limit on my old card to my new one, which has cash-back benefits.
**Me? A cheap "phase"? Ha!