For starters, not everybody can afford that kinda stuff. The comment you're replying to even talks about how his car only has a tape player and a radio. This cassette revival is primarily happening with young people who are in college or have otherwise low paying jobs (or no jobs). A lot of young people have old used cars with cassette players. For people in bands, as well, putting out music on a cassette is the most cost effective way to put out music physically.
And to address the bit about the phone, you'd be surprised how fast phone storage fills up with other stuff. My (admittedly several years old) phone's 8gb storage is more than half filled by system bloat so I have to use an sd card to put music on it. And that's not even including apps. This, unfortunately, isn't really an option anymore for the vast majority of phones (with the notable exception of most Samsung phones).
$5 gets you a gadget that will stream music from a headphone jack into a tape player in a car. I had one for my last car; it worked great. Or are these folks so poor they don't even have a smart phone? "Free with plan" Android phones can easily play tons of music. Yes they fill up, but many do have an SD card option.
Or you can spend $15 on an MP3 player (or pick one up at a thrift store for less). Considering tapes cost more than digital tracks, you'd save enough by buying digital to pay for the MP3 player and the cassette adapter by just forgoing a couple of tapes.
As to "cost effective": Blank tapes cost way more than blank CD-Rs. A quick search finds 30 name-brand discs for six bucks [0], and I've seen them less than $0.01 each in bulk. [0b] Tapes cost nearly a dollar each.
Almost everyone, in college or otherwise, needs to have a computer, or has access to one (libraries!), and most inexpensive computers have CD-Rs. If you don't have a CD burner in your computer, one costs less than a decent cassette recorder. $11.99 on Amazon will get you one, in fact. [1]
And it will be faster to make copies onto CDs, and the copies will be strictly better, than using tape.
Tapes are simply a retro "style" thing. They're not cheaper, and they suck. Trying to justify them in any way just doesn't work.
And to address the bit about the phone, you'd be surprised how fast phone storage fills up with other stuff. My (admittedly several years old) phone's 8gb storage is more than half filled by system bloat so I have to use an sd card to put music on it. And that's not even including apps. This, unfortunately, isn't really an option anymore for the vast majority of phones (with the notable exception of most Samsung phones).