A common complaint I hear at defcon and other cons in vegas is that the hotel internet is terrible. Hopefully good internet service comes as a result of this?
(benign) peak-to-average problem - I'll go ahead and just assume that defcon attendees use a lot more internet bandwidth than the average Vegas-goer, so during defcon the network is overwhelmed, but the rest of the year the capacity is adequate. Upgrading the links to satisfy the peak (defcon) traffic load costs the casinos significant money, but gives minuscule benefit since the rest of the year they only need to support the much lower average load.
(malign) the casinos don't actually want you to have good internet because they don't want you staying in your room internetting - they want you down on the floor gambling. Other non-gambling amenities (shows, restaurants, etc.) are mostly time limited - you only spend so much time eating, and shows are only a couple hours each - and can be a differentiator that draws people to a specific casino (because of specific food/entertainment preferences). Those people then spend the rest of the day gambling at that casino.
"Better" internet it's actually a negative differentiator - people who want to spend all their time infinite-scrolling will gamble less, so casinos don't want to attract them in the first place.