I don't really have a reason, but I keep seeing 3 new release threads a day with 500 comments requesting links...
You don't need to download every version, especially since most don't have major changes. You end up spending a lot of time updating and having programs break from being exposed to constant upgrades, creating artificial "bugs".
If you want to be helping testing, look more for new beta Windows 7 driver
and program releases, not Windows 7 builds. If you just want Windows 7 for normal use, find a stable version and stick with it for a while. Most of them are pretty stable... if you notice that one release especially has a lot of changes, or fixes a bug you have, then by all means upgrade, but otherwise don't be downloading the next build while installing one.
Do your part and test drivers
and programs. Those make up the bulk of Windows issues.