Trezors are critical for the mainstream adopters though who have no clue how to secure a computer.
Unfortunately, those computer-naive bitcoiners are also the most likely to fall for "social engineering" hacks, misuse the Trezor, and lose their coins in spite of it.
According to some estimates of bitcoin's wealth distribution, most of the people who own some bitcoin own only 1 bitcoin or less. The Trezor is not worth the expense for them.