unlike credit cards that have large equipment costs or subscription costs.. accepting bitcoin is cheap and free of contracts, thus even if they dont see customers use it for months, the business can still offer bitcoins without any worry about costs...
Unfortunately, that's not true.
There's a cost that comes with accepting Bitcoin, and that's mainly education, maintenance, controlling, bookkeeping. Those can easily add up to an amount where it's no longer justified to process Bitcoin payments below a certain threshold.
Also, under specific circumstances, where e.g. an online shop wants to offer a lot of different payment methods, the sheer amount of alternative payment methods may in fact lower the conversion rate of said shop. That's why shop designers usually don't want to clutter their shopping cart checkout with loads of rarely used payment methods.