Some home builders think it is a good idea to increase the dryer vent line from 4" to 5". I guess they think it will help with air flow. Unfortunately while the larger duct line will help when moving air in a HVAC system, it causes problems when used for dryer ducting.
The dryer exhausts not just air but is hot, heavy & moist air with lint suspended in it!
As soon as the dryer exhaust hits the larger diameter ducting it immediately loses VELOCITY and the lint begins to fall to the bottom instead of getting blown out the dryer vent exhaust.
Every time I have cleaned a 5" dryer duct vent line I have found a build up plug of lint where the 4" & 5" ducting are joined.