Have you ever done recruiting? It's incredibly time consuming, and in the vast majority of cases the recruiter executes a process that ends up with a "no hire" decision.

Companies can't afford to have their employees spending all their time doing the recruiting process so the key point of recruiters is to do as much of the work as possible to free the time of the employers.

Once the decision is established to use a recruiter, then which recruit4er an employer chooses to work with depends on corporate priorities. The larger the company, the more likely it is to have a human resources department and therefore the more likely to have a "recruiter selection process" that emphasises things like size of the recruiting company, global reach, breadth of services, time in business etc etc. These bigger recruiters yes, sometimes (but not always) have "tech recruiters" with no particular knowledge of tech. Smaller companies that have the discretion to choose to work with any recruiter are more likely to work with whatever recruiter they ,know through personal connections, or whichever recruiter last hassled them on the phone for work.