It's no different to any other bad design. It could be better.
All phones and computers can be completely powered down. They're hardly ugly switches.
They consume a lot less power, but leave an 'off' phone in a drawer for a month starting at 100%, it will not be 100% when you 'turn it on'.
They all self-discharge [1], some chemistries more than others of course but phone batteries certainly do.
I'm thinking the battery goes dead because of leakage currents through the rest of the circuits, which were probably not designed to the nA standard.
A solid-state Off switch would also need a good silicon device to cut current consumption at the battery. Which also costs something.
This is an emotional, low-quality response to what is a measured comment actually providing nuance to the discussion.
The parent poster is very clearly not saying that leaving off the power switch leads to a better experience for the consumer - they're just giving legit reasons that a design/marketing team might use to justify doing so. Please don't try to cheapen the knowledge that they provided like this.
Where 'maldesign' is my dad's favourite word for every seeming design flaw or 'unreasonable' limitation. (-:
iPhones (and I assume most Androids as well) can't be completely powered off. Neither can Macbooks. In fact, I'd guess that most modern digital things with non-replaceable batteries can't be powered off.