Shell command history is truncated to 10K commands on installation

Describe the bug

Shell command history is truncated to 10K commands on installation. Super annoying, especially for people who have long and rich command histories

Steps to reproduce

user@laptop ~ % echo $HISTSIZE
10000000
user@laptop ~ % echo $HISTFILE
/Users/temporaryadmin/.zsh_history
user@laptop ~ % wc -l /Users/temporaryadmin/.zsh_history
   66033 /Users/temporaryadmin/.zsh_history
user@laptop ~ % sh -c "$(curl -fsSL https://raw.github.com/ohmyzsh/ohmyzsh/master/tools/install.sh)"
Cloning Oh My Zsh...
remote: Enumerating objects: 1295, done.

<removed>

Looking for an existing zsh config...
Found old ~/.zshrc.pre-oh-my-zsh. Backing up to /Users/temporaryadmin/.zshrc.pre-oh-my-zsh-2022-05-03_11-50-17
Found ~/.zshrc. Backing up to /Users/temporaryadmin/.zshrc.pre-oh-my-zsh
Using the Oh My Zsh template file and adding it to ~/.zshrc.

         __                                     __
  ____  / /_     ____ ___  __  __   ____  _____/ /_
 / __ \/ __ \   / __ `__ \/ / / /  /_  / / ___/ __ \
/ /_/ / / / /  / / / / / / /_/ /    / /_(__  ) / / /
\____/_/ /_/  /_/ /_/ /_/\__, /    /___/____/_/ /_/
                        /____/                       ....is now installed!


Before you scream Oh My Zsh! look over the `.zshrc` file to select plugins, themes, and options.

• Follow us on Twitter: @ohmyzsh

<removed>

➜  ~ ls -d
.
➜  ~ echo $HISTSIZE
50000
➜  ~ wc -l /Users/temporaryadmin/.zsh_history
   10017 /Users/temporaryadmin/.zsh_history
➜  ~

Expected behavior

Don't truncate the history file or AT LEAST back it up

Screenshots and recordings

No response

OS / Linux distribution

MacOS 10.15

Zsh version

5.8.1

Oh My Zsh version

master

Terminal emulator

iterm2

If using WSL on Windows, which version of WSL

No response

Additional context

No response