If you could spend just one outing in the field with me, I think you would understand why build quality is important.
My 50D is now almost unusable because after getting knocked around for so many years it's buttons barely work anymore. . There's so much grit and stuff worked in behind the buttons and dials that they can barely be turned any more. . The shutter button - it takes a near-herculean strength just to get it to go down far enough to take a picture.
My 5D barely works either, but its problems are more electronic in nature, not so much physical. . I think that constantly having it out in rain and snow has finally caught up with it. . Some of the modes don't work, and you have to hold buttons down and implement weird menu options just to "trick it into" focusing and taking a picture.
Also, the mounts wear out from taking lenses off and putting them on so much. . I have to send the bodies and lenses in to Canon every few years to have new mounts installed because after so much use the metal wears out and the lenses are loose when mounted on the camera. . Sometimes this is so bad that the contacts don't work and it won't autofocus and the Image Stabilization gets weird because power to the lens is cut off abruptly when trying to shoot. . This isn't just the mount screws coming loose - it is the metal of the mount itself wearing so thin that there is sloppy play between the lens and the body.
And another thing with the lenses is that the zooming mechanism and the tripod collar gets all sticky and hard to turn because of the lenses getting knocked around and dirt and grit getting down in there inside of the parts that rotate.
And the catch that keeps the battery in the camera - the "battery door", if you will - breaks from being opened and closed so many times, and then the camera won't work until I get a new one. . This isn't a problem with 1 series bodies because the battery catch is on the battery itself, and when it breaks then I just use one of the other batteries.
So I guess that yeah, build quality is very important because the two cameras that have fallen apart on me are the ones that aren't one series bodies, and the two one series bodies that I have had, they have seen much more use, and yet they remain perfectly functional when treated the same way and when used in the same conditions.
Well, I asked, and that is an answer. In your case, with your use, you wear them out. You need good build quality.
Me, I take 10's of thousands of photos and my cameras show hardly any wear. The lenses are pristine and don't even need cleaning except maybe once a year.
BTW, it's its.