Many small business owners are idiots and obsess over tiny sums while being blind to large costs. And they loose far more customers by not accepting payment methods than they save in fees. In your own example it's only €41 per month that they save by turning away who knows how many customers.

Another example is small B&Bs who happily pay 15% or more to third parties like booking.com, but think it's outrageous to pay 2-3% in card fees to accept bookings on their own website.