Yes, and no. Theft can be a strong possibility, but not "all the time". It depends a lot on where you lock the bike, its value, and how you lock it.

I have had two bikes stolen twice in about 10 years. One was a hybrid worth about $1k. It was locked with a cable by the side of a Walmart in a neighborhood of questionable reputation. It took me about 15 minutes to get in and out and the cable was cut when I came back. The other was also a hybrid worth about $1k. It was stolen while locked with a cable, in the underground garage of my building. However I have another "cheap" bike from a big retail store locked with a very cheap cable lock in the same garage, and nobody stole it.

So now even if my contract says I can't bring a bike in the apartment, my "expensive" hybrid takes the elevator with me and stays in my living room. I also now use a thick U-lock because cables are risky. But even then I know very well that leaving it locked with a U-lock outside for any prolonged period of time is also risky.

If you have a "nicer" bike than average, you have to be mentally prepared to have it stolen at some point. Not "all the time", but maybe a few times in your life, depending on your luck and locations.

Speaking from experience, no, they really don't.

As LPL will tell you, you don't need to have the most secure thing on the planet, you just need to be a hard enough target that the thief gives up or picks something else.

If you don't lock your bike, sure it'll get stolen from some places.

Bike theft is a crime of opportunity. Nobody is stalking a specific bike to take, it's usually "oh shit there's one that looks easy imma take it"

I have a hardened steel U-bolt lock and a thick AF cable (do not get any cables under 1/2in as they can be easily cut with side cutters or even good wire strippers) the U lock goes through the frame, the cable and disc lock go through the wheels as well. I also like to take my seat with me in my bag, since nobody wants to ride a bike without a seat.

I never had a bike stolen even during the few years I was using one as my main form of wheeled transit. It helped though that I never had an expensive bike, always locked it up when I left it (average cable lock), and had somewhere secure to leave it at night.

It's illegal where I live to lock a bike to "urban furniture", and a pole is also often not the safest place. If not stolen, it will be removed by the city.