AFAIK the concept of legal tender doesn't mean that you can use the law to force a business to accept dollar bills. If you want to trade your black lotus for my foil charizard, I can't refuse to trade and then sue you to pay you in cash instead. Rather, AIUI, the "debt" referred to there refers to legal debts, so e.g. if my dog gets into your chicken coop and you sue me for damages, you can only ask for an amount in dollars rather than forcing me to provide you with replacement chickens.
IANAL, and I don't think the GP's argument is valid, but his goal is valid: retail businesses should not discriminate against people without phones or credit cards. There are lots of them, and it could be you at some point. There are lots of good articles about accessibility and how we all get old, etc. That same argument applies here: you may be well off, consider having a smartphone and several credit cards "normal", but you may fall, financially, and you will lose those things. I would call this "financial accessibility". The argument is NOT for the business to address more market (there is that though) but rather to avoid making life even harder for people who's lives are already quite hard.
Retail businesses that don't accept cash are also reducing their risk of being robbed. Prominently placed signs informing customers and criminals to the lack of cash on site means most criminals will go to the next place. It also helps keep the employees' sticky fingers from skimming the till.
Yeah, I have been on both sides of this issue. I really want cash to work anywhere, but I have also worked retail and seen that cash is a giant pain in the ass for businesses. It has to be secured, transported, the employees steal it, and it means more accounting headaches. Whereas if all your payments are done through Square, this all goes away. It's not surprising to me an increasing number of businesses— especially really small ones like food trucks— are just doing away with it. I'm not sure what the solution is.
Also, making change for cash transactions is also not trivial. I've been on both sides as a vendor and a buyer where this has been an issue. As a vendor, i've tried rounding down to be advantageous for the buyer for the inconvenience, but it's annoying. as a seller, if it's a craft fair or some sort of thing with small artisans, i've rounded up for a tip. either way, it's a painful part of a business that going cashless avoids altogether.
Not many retail places are building their own locations any more. Normally, they are just renting space. The things you mention are the landlord's problem
Edit: also, landlords are not doing these things because they are "right", they are doing them because they are regulated to do so
Landlords don’t provide parking ‘because it’s right’. A more accurate statement would be ‘because it is required by the Americans with Disabilities Act and you won’t receive a building occupancy permit unless you provide handicap parking’.
The issue is that there is no debt if you haven't yet transacted. And you can't steal the item and then claim to be in debt and force the person to take your money.