I don't make the change because I have no motivation to make the change. My current gear answers all my wants. Sometimes, we go out back and play frisbee catch with our standard poodle. It can be a challenge for me to catch well focused shots of the dog in action, but I attribute failure to my lack of skill in shooting that sort of action. It's not the camera, and I don't really value the resultant successes enough to get GAS over the shots that i miss. I own lenses that will allow me to catch photos of birds in flight, and I have had some success, but locating and getting out to places where opportunity for good shots of birds in flight is high is a bigger challenge than taking the photos.
My gear is no impediment in my attempts to capture the type of shots that are important to me, holiday photos of my family, photos of my grandchildren doing whatever (most action type shots). The image quality that my gear provides will compete with any of the newer cameras. More importantly, the display methods in fashion today require that I downsize my photos, so rarely do I the opportunity to share photos at the highest quality that I can achieve.
For all the above reasons, I'd rather spend my time taking photos than acquiring and learning new camera bodies.
Each of us is different. I have been through my GAS stages with photo, video, and audio equipment. I enjoyed that stage, but I am over it now. What went a long way to dampen my enthusiasm for new equipment was the realization that the latest greatest never stayed that way long, and, while I always tried to buy the best I could afford, spending money did not always translate into gear that held up well.
I purchased some really high-end prosumer video gear back in the day, shot a lot off video on holidays and vacation trips, but the gear literally rotted while in storage (not rot as in rusted or grew fungus, it just stopped working), and then I was left with a worthless brick.
Nevertheless, I feel we should all enjoy our hobbies and/or our work no matter our stage with respect to GAS.
Happy shooting.
Caruso