Something that needs stating in this debate is that any on-bus OR off-bus ticketing comes with a cost. If the SME operator has only one or two routes, they'd need only a few ETMs. It's a while since I was involved directly, but in 2020 the price of one Ticketer machine was around £3k. On top of that was an annual fee for the software, which came at several levels, and of course at several prices (and I can't now recall what they were). If you wanted an app, then you bought one off-the-peg, which obviously came at a price. You could sign up to a season ticket e-ticket provider . . . again, at a price. And the cost in time and effort to actually load the fares and update same . . . and that isn't simple . . . I know of one LTA that has 5 or 6 variants of a child discount card; same fares, but they have to be uploaded individually!!
My point is that, for an operator that sells few tickets; whose business is mainly contracts and ENCTS passes (and there are many operators like that), this is all an extra expense that is unlikely to be recouped other than by increasing fares. Yes, it is necessary to have some kit to comply with BODS, but actually such investment is likely to affect profits. I know of one operator who folded because they couldn't justify the expense, and used an Almex machine until the end.
Cash fares are cheap to administer. I'll also make the point that some passengers (I refuse to call them customers!) actually only have cash . . . they are paid weekly in cash, and prefer that as they can budget easier that way. Not everyone has a smart phone, or can use computers . . . and dare I say that these folk are also predominately bus users.
I don't want to get into a back and forth debate, but please remember that one size really doesn't fit all. We've seen what happens with the threat of closing station ticket offices, and forcing passengers to buy from remote machines or on-line . . . and we seem to be discussing exactly that here!!