I've dealt with Cruz's office and they are extremely rude and condescending. They accused a visitor of being an "out of state agitator" and all she did was stop in to Cruz's local office by herself. She was very polite. When I visited his office, the staffer didn't bother to take a single note. The staffer told me that they are very busy with numerous visitors. (Yet, the visitor logs showed only 4 names in 3 days) I have emailed Cruz numerous times and have never received a reply. Basically, I did not feel respected by Cruz's staff.
I received more respect at Lamar Smith's office than at Cruz's and I don't even live in Lamar Smith's district!
I haven't utilized Cruz for any constituent services, but who knows maybe he is "top-notch" and that is why he is popular.
On the other hand I utilized Cornyn's constituent services in 2005 and they were excellent. (I think I might have previously dealt with Cornyn when he was AG of Texas or something like that) When I started emailing Cornyn at the beginning of Drump's presidency, his staff did take the time to respond. When I visited his office twice after Drump became president, his staff was polite and took notes. I other words, I felt I was respected as a human being.
I dunno, maybe Texans prefer rude and condescending. This is a state that favored Cruz and Patrick over vanilla bland, David Dewhurst.