I am a Slabjack contractor and only about 5-10% of the slabs we raise even have rebar. The vast majority were just poured on native soil or uncompacted fill. Porches aren’t pinned to the foundation, garage floors rarely have control joints, It’s just shoddy workmanship and results is way too much settling and cracked slabs, don’t get me wrong, I’m happy for the never ending work but there are a lot of unhappy homeowners when concrete is settling in the first year or two.
Typically site preparation is not the responsibility of the concrete contractor, but part of the site contractors job. If the job superintendent does not make sure the proper preparation is complete prior to scheduling the slab/flat work then the concrete contractor is not at fault. Additionally the concrete contractor is happy to oblige the superintendent as he knows he is relieved of all liability due to improper site preparation. This type f work is usually the result of the general contractor underbidding the job, and making up for it in the quality of the work and lack of materials. It is very easy to hide such cost saving measures in the concrete work, since once concrete is in place no one knows about the shoddy work.
I place the blame squarely on the property owner/manager for only taking the bid amounts into account when selecting the general contractor, and poorly written bid specifications.
My personal experience after being both a general contractor for 20 years and a concrete contractor for 14 years is that most will not pay for a job to be done correctly. It goes back to how the backfill was done. Most often site prep as mentioned in the previous answer is not done properly. Concrete contractor comes in and follows shoddy work.
My experience with reinforcement is that even when a builder/contractor is willing to step up and pay for rebar that it usually is not installed properly. Most of the tear outs that we have done that do have rebar in the concrete usually fail to have it closer to the center of the slab. Most of the time its at the bottom and in the dirt.
Pinning flatwork to foundations typically voids a homeowners warranty on a new build here in Colorado. Slabs are meant to be able to move independently from the foundation. In Colorado we are seeing haunches added to the foundation for the slab to sit on to help with slab settling.
Not all concrete contractors cut corners. If you hire the cheapest you will get bad work. Not all contractors cut corners.