I’ve just looked through the changes for the new season and when I saw the new gank paths for top and botlane it hit me: Would you really want to send your adc+ support to the lane that’s much easier to gank? The new map changes mean that toplane is way harder to camp, so giving that advantage to your due lane makes a lot of sense! Just put a toplaner that’s good at surviving/deffing tower in 1v2 in bot and you’re good to go.
But it doesn’t end there. What else changed? Void Mites! If your ADC and support are top, it makes it easy for you to contest this early objective and get tower plates. Then when plates are gone, they take the new and stronger rift herald and swap back to botlane with herald and a gold lead, ready to crush that lane too. At this point the enemy botlane (if they didn’t swap) will have maybe taken down 1 dragon. Absolutely no problem for the team who swapped.