Price/cost is the last thing you compete on unless you have a wholesale advantage, which nobody in this particular industry does (visa/mastercard set core rates)

Source: I’ve worked with higher ups in numerous commerce operations.

Commerce is actually even worse than many realize. Look up pepsi and walmart as a small example.

* it instantly brings them a ton of consumers * they have capacity to serve those customers

if they don't competitor can just keep higher price (especially if it is just small middleman fee most people might not care that much about)

And even if both of those are true worst possible case is them expanding to handle influx of customers and then competition following in few months, making their investment moot