I would respectfully disagree with that it is NOT free. Its part of the amenities that Disney charges a premium for. When they had cable modem service and we set up our own wifi in our campsite and we had no problems establishing and keeping an internet connection. Also, we still continue to stay at various Disney resorts throughout the kingdom and have far far less problems, and we set up our own private wifi in our rooms on top of that. Although I do agree that during peak hours it can slow down. However, a popular misconception is that streaming causes a huge drain on the infrastructure. Streaming requires far less data usage than people realize. I'm a cord cutter so I know all about data usage! When we regularly have 24 devices connected to our home wifi we still have speeds regularly over 200gb's so its entirely possible to have a proper wifi set up and functionable, actually expected at a premium campground. It is afterall 2017, not 1999 waiting for dial up to connect!! Did I mention that Disney charges a premium for their campground!!
Wifi in hotels is much different then Wifi at the Fort. Hotels (generally speaking) are much more compact and as such it's generally easier to locate WiFi antenna to fully cover the area with good signal.
The Fort is much more Geographically disperse and as such, it's more costly to have the antenna's set with a good overlap. Additionally, weather conditions are now a bigger factor.
Speed of the network depends on A LOT of things, particularly with WiFi. The quality of the signal (and not just strength) is a HUGE factor. You could have a strong signal but there could be interference (i.e. static in the air) which causes more errors which requires re-sending of data (error checking) slowing things down. Of course the amount of users on line at the same time is a huge factor.
Back to Ed'S "Super Highway", the merge on/off may be slow but once on you can move quicker, but adding to the analogy, Have you ever gone to Maine? We were going to Acadia Park (beautiful by the way) and by the map, it looks like taking US Route 1 would be the quickest route... certainly the shortest route versus taking I-95 North of and then cutting across and down to Acadia. However, when you take 4 lanes of traffic (one direction) and shove it down to 1 lane.... You are bound to be in a back up.
So you have (Potentially) the fort usage being increased couple with potential problems on the ISP side.... Well, you know how it ends.
Me... I don't do a lot of "Streaming" while I am at the fort/wdw, so that's not an issue, but I do end up doing some "Work". I usually just end up using my phone as a hot spot. It's more secure, quicker and more reliable overall.