Why does nobody talk about the $7 airport parking lot 2 miles away

I flew out of Portland last month for a 4 day trip and almost paid $96 to park in the garage at the terminal. Then a coworker mentioned there is a city owned lot about 2 miles down the road that runs $7 a day with a free shuttle every 15 minutes. I did the math and it came out to $28 total instead of $96, which is just insane to me. The shuttle took like 8 minutes and dropped me right at the departures curb, no stress at all. I keep wondering why this never comes up when people swap airport parking tips, everyone just talks about off site garages that still charge $12 or $15 a day. The lot was half empty too, so it is not like it is some hidden secret that fills up fast. If you fly out of PDX, look up the economy lot on the city website before you book anything else. Does anyone else have a cheap lot like this near their home airport, or is Portland just weird about it?