they really are not meant to wear like shoes- all day-
they are kind of for at the beach- camping- when you are taking showers in camp ground showers and don't want to go in bare feet- when you come out of the lake- want to walk up to the car- you slide into them- they are for those (moments) in the summer time- they have no benifits when it comes to foot health- they are simply an easy slip into for a minute foot protector- protecting your feet from (community fungus) gravel roads- ect.
used to be sold as (shower shoes) somewhere along the way people decided they were great for beach/camping wear- from there over the years i bet lots of people have (tried) to wear them as if they were a pair of shoes- but as you found out- they are not- and were never meant to be. hopefully you can use up the 'bunch' you bought.
my granddaughters buy them for $1 a pair at the dollar store- then decorate the straps with fabrics or yarns- they get very creative with them- and they share them with their friends when they go to the beach.