The way I see it is that all the affordable compact cars skimp somewhere to stay affordable that makes it so it almost evens out with the competition in that class segment.

Carolla, you get class leading reliability and mpg, everything is just so "car" about it no thrills, just your ol' workhorse. You can even now get in AWD, BUT you get lack of more modern tech, as well as a very cheap interior even for the class segment.

Civic, you get 3rd place reliability, as well as second place for mpg, but mostly, especially in Hatchback form but also in Sedan form, you get the best amount of storage both for cargo but also for your everyday items in the front seat as well as decent driving dynamics and decent tech. BUT, sound deadening lacking even compared to the Carolla, paint quality sucks as usual, and the safety ratings are....serviceable, given the modern safety requirements.

Mazda 3, you get second place for reliability, you get a VERY nice interior given the price point and driving dynamics are amazing. BUT the ride is harsh due to Mazda's zoom zoom philosophy and because it's cheaper than providing a softer ride, and you get probably the least amount of space for anything whether in sedan or Hatchback, out of the options and visibility SUCKS. MPG compared to the competition is also lackluster and Mazda still uses their trident and true 6 speed as well as NA Skyactive as the default engine option to save on production cost of having on not having to make their own CVT or new engine design to improve MPG.

Snentra, up until recently, was the second most economy car ever, for the US market (RIP Versa), you sacrificed everything just to get the cheapest price OTD and good mpg, reliability meh, ride quality atrocious, interior cheap and rattley, tech also meh (in comes the new gen here), but hey you could get it for stupidly cheap and anywhere would finance you for one regardless of your credit and it was transportation.

Elantra, you get class leading tech in this segment of car, interior that shines above all but the Mazda, and above average MPG. It's the most modern of the bunch, BUT your reliability is underwhelming to outright bad as build quality remains inconsistent with Hyundai and Kia vehicles, ride quality is above the Sentra but below the other 3, it's harsh in a cheap way rather than with at least some purpose/ intent like the Mazda 3, storage is average, and the drive is probably 3rd place for least inspiring. But again it's a modern economy car that actually looks somewhat pleasing on the eyes.

The point being, is that the reason people default to the Carolla/ Civic even today despite the higher prices is because they are the most well rounded of the bunch, they are economy without being outright poverty, they are economy without trying to be sporty and harsh, they are economy without trying to be the flashiest with the most tech. They are economy for people who want something that does a little bit of everything okayish rather than specializing in one area.

What is and is not a great deal depends on the buyer's preference here, yes, the Elantra or Mazda 3 or Sentra can be had cheaper than the Carolla or Civic but you have to sacrifice something for it, and the average buyer hates making long lists of pros and cons and doing research so they just stick with what they know and with the vehicles that just do everything well even if it means spending a little extra.