Except mums with pushchairs. And people who can't climb the steps to
the lower saloon. Many of the complaints regarding double deck
low-floor buses related to the early vehicles which had little seating
in the low-floor area.

Oh the modern ones still have problems too. The seats at the rear of the
bus are often up high steps that make them as inaccessible as the upstairs
(and even for those that can use them extra care is needed when going to get
off the bus, I've lost footing a few times myself). The side facing seats
often found near the front are not deep enough and have inadequate hand
grips so when the bus turns corners people are catapulted across the floor
of the bus. When the wheelchair areas are not in use the hinged seats will
often quickly spring up without passengers realising so if they drop
something and go to pick it up they end up falling to the floor.