Trackers just seem to come along for the ride for what you might consider normal services. Ad networks and analytics packages. When Sprint (or whoever) wants to run a campaign, they add their own pixel to for auditing purposes, to make sure they are getting the right number of impressions. What also happens is if one ad network doesn't have an ad, they send it onto the next ad network, and each of those have to "track" to make sure they don't deliver the same ad to the same person more than X times, etc... Rinse and repeat, and that's how you end up with so many different pixels firing. Aside from that, there are legitimate/intentional "trackers" -- like analytics.
We do offer an ad-free experience for relatively cheap via account upgrades:
https://forums.macrumors.com/account/upgrades
We are revamping this paid option and hope to relaunch it in the near future.