Why is my WordPress website using a constant <400MB RAM even when I disable all plugins and use a basic theme on shared hosting?

 a) from php.iniHow do I set memory limit in WordPress?Here's what you need to do:

1. Locate or find your php. ini file. ...
2. Use your favorite editor to open and edit your php. ini file.
3. Look for the line that says 'memory limit = 32M'.
4. Change the 32M or some other number to the desired limit (e.g. 256M or 512M).
5. Restart your localhost or server after saving your changes.

 b) Edit wp-config.php and increase wp_memory_limitIf you’re running low on memory, there’s a simple solution: increase the amount of memory you have access to! WordPress lets you set the current memory limit in its  wp-config.php  file  via the  variable. However, this limit may be less than the amount of memory provided with your hosting plan.