Because I can fix bugs.

Years ago, I found a replicatable bug in Adobe Photoshop (CS2?) that required me to delete my config everytime and set PS up how I liked it. Adobe's acknowledgement took two weeks, then a month of triage, followed by a "Yes, we'll have it fixed in the new version when it ships. You can pre-order an upgrade for only $lots" and new version shipped 6 months later.

Yesterday I found a bug in a framework I use. Within 2 hours I'd found the line of source code responsible, fixed it and was on my way again.