I mean, why not? I run a few small sites and even I throw a 4096-bit key in there on 'em. It's not a burden.
It's a burden on the DNS resolver side. 4096- or 8196-bit key operations aren't exactly cheap - and the time taken for the public key operation grows superlinearly with the bit count (depending on the specific variant of the modpow algorithms in use, somewhere between O(b^1.585) to O(b^2)).
Not to mention that on a slow resolver it might even trigger a time out and a SERVFAIL.
2048 was considered "long" not too long ago, and it isn't now. Perhaps someone is trying to stay ahead of the treadmill. :-)