There's a simple answer to this potentially deep question: bots. Activision hasn't commented on the existence of bots/AI enemies in Call of Duty Mobile, but it's obvious that in the early levels, you're playing almost exclusively against AI enemies set to a very low difficulty.
Call of Duty: Warzone Mobile is an upcoming first-person shooter game developed and published by Activision. It was announced in September 2024. In November 2024, the beta version launched in Australia. Currently the beta version is available in Australia, Chile, Norway, Sweden and Germany.