nostr:npub1l3xmflqy6j2hyr00m88zl3yq7lvt6630t7ql6dujy2d52dfv5ggsrzpp9z 

Having done no research into the current situation, I would guess heat. Bed bugs do better in the heat, I think that's often linked to periods of high bed bug activity. 

Not sure if "major cities" means global or US, but maybe with rent and housing crunch in many US cities, people are also less likely to move, more willing to move into poorly maintained buildings, etc. More shitty furniture flosting around. That's speculation.