Call of Duty has increasingly shifted to games as a service model and this is not making it easy to be a retail buyer. Modern Warfare is no different here.
Call of Duty: Modern Warfare file size is wildly different depending on where you want to look at it. It was listed as just over 60 GB on the PlayStation Store while Xbox One version has been discovered to be as large as 137 GB. The PC version meanwhile had a requirement of 175 GB, which makes it rather large for a game on PC even next to Red Dead Redemption 2.
The game is now up for pre-load on Xbox One where it is divided into different packs with a varying file size between them, but apparently there is still a massive day one update that has to be downloaded even if you have bought a retail copy.
Just like it is the case with Black Ops 4 last year, Modern Warfare currently has an update that is more than 40 GB in size on the PS4. This will be required by those who purchase a retail copy but with a digital version, the player should be able to download the game along with the update.
As time passes, it has started to become meaningless to get the retail copies of games that work more as a service and get updated frequently. This applies to something like Destiny 2 or Battlefield where the retail code that is present on disc is outdated and large updates have to be downloaded either way.
When it comes to day one update sizes, The Outer Worlds is one of the recent examples while Death Stranding is quite small and a rarity to see these days. Modern Warfare is more of the former instead of the latter.