In my experience designing electronics, EEs and the people handling logistics/manufacturing are extremely risk averse actors who make many decisions based on trust and personal relationships. As a contractor, my deadlines would often only allow for at most two or three prototypes before I had to deliver a working design and that did not leave much room for error. If my client or I had an existing relationship with a vendor that always supplied parts on time, fast samples/dev kits, or if I knew their reference designs to be more reliable than most, then that vendor would be the preferred source for parts even if their other offerings weren't the best or the most cost efficient.
You can also often get great pricing for low/medium volume orders if you have built up a history so I've had situations where I had to design a significantly more complex board with a microprocessor that normally cost 10-20 times more than the CPU I would have chosen (from another vendor). The client's supplier for the other most expensive part on the board had too much inventory of a soon to be discontinued processor (that was pin compatible with a newer one, also very expensive) and the account manager's boss was willing to sell us everything we needed at an 80% discount off high volume pricing with pricing guarantees on the newer parts for several years, all to meet some regional sales quota.
As another example, microprocessors often have arduous power up requirements where different voltages have to be supplied in a specific sequence within annoyingly specific timing tolerances. In a project using Marvell microprocessors, it was much faster to just use Marvell's power chips and existing reference design than to waste precious time on modifying designs for cheaper chips from other vendors. The power parts cost five times as much as they would had I chosen my favorite vendor but because the board was a mixed signal design it was extremely expensive to make changes and test prototypes.
A vast catalog of parts is an especially powerful market force if you are a company like TI that has a well developed software tool like WEBENCH which can spit out dynamic reference designs for most of their power chips. Unless I have an existing reference design from a vendor of a major part (like the CPU above), I usually go straight to TI's tool to design any power supplies I need so I can focus on the meat of the PCB. If TI also has parts that do something else I need on the board I will often just choose them instead of researching other vendors (unless it's a really expensive component) and that compounds as I make more and more PCBs, each time becoming more comfortable with TI parts at the expense of others.