I mean, it's a bit of both. But why would fly rods be standard in 4pc while gear rods aren't? It's because a fly shop ordering rods 2-3 at a time can't eat the $50+ in shipping to ship an oversize length tube for a single rod.Huh! Interesting, not something I would have considered - I thought "travel" was the main reason for shorter rod pieces (4 V. 2) so your comment debunks my understanding. Your comment makes sense from my perspective as I've traveled on an aircraft with fly rods exactly one round trip. On that particular trip, with Alaska Airlines, I saw tubes carried on that were five feet long (Alaska bound); I think AA was generous since my guess is 90% of the travelers were either hunters or fishers. Given your comment, Mr. B., it would be nice to have more two-piece rod options as I hardly ever break my four piece rods into four pieces, they're always in my "two piece" rod bags.
Then, consider how many rods are sold through mail order from the dealer to consumer - it's a massive percentage these days, and most small business fly shops can't offer free shipping to be competitive on 1pc and 2pc rods.
So 4pc rods are standard, and the end consumer gets something that's easier to travel with.