Bottom line: In an in-depth YT interview with TeeP about the future of Warzone, Josh Bridge, CoD's live operations lead, acknowledged Warzone's huge install size and shared that the game lost players every time a major map update was pushed. Pulling out Caldera for Verdansk, Bridge remarked, was essentially like re-downloading an update the size of Warzone.
Keeping content fresh is vital for live service titles like Warzone, but CoD's free-to-play BR has particularly suffered from massive file sizes, both while installing (175GB on PC) and during season updates. More if you've got Modern Warfare installed as well.
Although multiple patches have trimmed GBs from the game's overall size, the bloated state of Warzone means that it's still a challenge for devs to balance map rotation while keeping update sizes manageable.
Ever since the introduction of Caldera, Warzone's big map that replaced Verdansk late last year, players have (unsurprisingly) wished for the latter map to return. Cycling between the two areas is also what Josh Bridge, his team, and everyone else wants, but it is simply not feasible due to technical limitations.
While map rotation is certainly possible in Warzone's current state, which already gets regular season updates, actually taking out Caldera and putting back Verdansk would essentially result in a download "like, the size of Warzone," commented Josh. The move also threatens a declining Warzone's playerbase, as gamers simply quit or uninstall the game when they're forced to download a major update, not to mention the frustration of last-gen console players with storage constraints.
Josh shared that the devs were putting a lot more effort into how they can make map rotation possible by sorting it out on a technical level, ensuring that Warzone remains fresh and has variety of experiences to offer.