Drive by wire is actually less complex than traditional.
STEER-by-wire, however, adds complexity. And the short-term risk of a failure is much greater in your steering than in your throttle... even if you can't turn off the engine you can at least take it out of gear and let it redline itself into oblivion. Power assisted steering adds complexity but it's a backup system the way it's implemented, which means you can still steer even if the power system stops working.
Things should be designed to "fail gracefully" where possible, not catastrophically. Losing your car's remote control means you can still unlock, start, and drive the car in the traditional manner - IF it has traditional keylocks. Otherwise you are standing outside your car with very few options. Losing power steering means you can still steer the car. Losing steer-by-wire... well, who knows?
I have a related story that happened to my wife and son a year ago. Background: Toyota makes the only minivan in the USA that offers optional AWD, and we live in snow country so AWD/4WD is an absolute requirement. Trouble is, to make room for the rear differential Toyota jettisoned the spare tire (!!!) and deliver the vehicle with runflats (!!!). Those are about 2X as expensive, drive horribly, and only last about 30K miles, so we had the local tire shop replace them with four top-end traditional radials and bought a spare wheel with a spare tire mounted on it, which we carry in the back end. Returning to the story, some object in the road took out a tire in the minivan. This was very late at night (of course) during an intense snowstorm (of course) while I was out of town (of course). But my family is self-reliant so they broke out the jack and got the bad wheel off. When they went to mount the spare, the wheel had some sort of decorative cover over the lug holes - which was held on by a special screw requiring a special tool! They called me from the side of the road, across the country, and I seriously could not understand WTF they were saying because how can it possibly be that they can't "get to" the lug holes on a car wheel? They finally hung up in frustration. The story is long, but the short version is that they ended up having AAA trailer the car to the tire shop at midnight. The next morning the tire shop's response was "Oops". It also turned out that the lug holes were so deep and narrow that the factory lug nuts wouldn't even fit. Needless to say, when I got home that wheel cover had a serious and permanent accident... I confirmed the wheel actually fit (something I should have done earlier)... and I required the shop to provide a dedicated set of lug nuts free that now stay with that spare. All of this was a result of "unnecessary complexity", just exactly like a keyless fob with no mechanical backup key.