I do think have every right to be annoyed.
As you say though, it is the communication that is the issue, that is what I am annoyed with, not that they have lots of work elsewhere. Price me out of the quote, timeline me out of the quote (i.e I am booked up till November....2022), or tell me direct, the job is too small for their firm or compared to available work. One builder did the latter to me over the phone and I thanked him for being honest (although he did specify angle irons so I was not too bothered).
I do not begrudge a firm for having easier work by any means. But the delay caused to me for waiting on a firm that will not communicate is just damaging, annoying and frustrating.
The one UPVC firm that did this to me caused a delay of 2 months. All because they did not want the work, but refused to say that to me and felt it more appropriate to string me along until I gave up.