My bank sets the default to "Standard (1-3 Days). Many forget to click the checkbox. I have also heard: "I only do instant when I need it" implying some implicit cost/limit they fear. This is probably still worth it for Banks. As not _all_ transfers are now the dreadful super expensive instant variety.
It's a dark pattern, my bank does it too. Reminiscent of online stores that put the price-sorting option "High > Low" before "Low > High", as if literally anybody would ever want to do the former. This is a heuristic I use to judge trustworthiness. Decathlon doesn't do it.