There's a lot of reasons why I and a lot of others would do that, and none of them include saying that what the engineers did wasn't good enough.
First off, modding can change actually very little. Usually tuning and maybe some parts, but the underlying driver design is, most of the times, left alone (unless you're talking about T50 mods).
I have a problem when ever I tinker with stuff " bad juju " happens. I did not mean to insult anybody, I actually respect those of you who can do this as I have really really low pickup when it comes to the mid/highs as in almost none. The MSR7 sounds (pun intended) like what I want.
Now if I could find one in Canada that cost less than $250 Canadian
Secondly, you can take a hugely capable headphone, like the MSR7, and tailor it to your liking. Its tuning wasn't quite right for me, so I tuned to something that I find better. The fact that it allowed me to do that and that the result was great just goes to show how great the engineers' work was, not the contrary. They just stuck with a tuning that didn't fit my needs quite right, simple as that. Now, couldn't I have bought a different headphone in the first place? Sure, but none of my options were technically as good as the MSR7, so I'm glad I went that route.
Third, sometimes trying to solve one problem, you create another. My biggest gripe with the MSR7 was the comfort, as my ears protrude a bit too much and would touch the drivers. Combine that with a high clamping pressure and the headband that creates a hotspot at the top, and I couldn't use them for long. So I tried using HM5 pads and these fixed the comfort, but they destroyed the sound. Then I opened the headphones up to try and fix the sound while keeping the HM5 pads, and so on and so forth. My original target wasn't sound, it was comfort. I would've been happy with the stock sound too, I just prefer how it turned out.
Finally, and probably most importantly, it's fun to mod stuff. Maybe it's not for everyone, maybe it's not for you, but taking something, messing with it and making it mine is something I find deeply satisfying. It has nothing to do with disrespecting the engineers' work, nothing to do with me not liking what I got, I just like getting my hands dirty. From simple stuff even, like changing pads or getting nicer cables, that's modding. The extent to which you do it is mostly irrelevant, what matters is that you enjoy the process and, hopefully, the end product.
Cheers!