This could be caused by many different things, as well as a result of a broken cron setup, where actions are being scheduled, but never run.
The best way forward is to try and understand what is actually being scheduled or rescheduled, what are the action names? If you can find the action names, you’ll be able to pinpoint it to a specific plugin or theme (or core for that matter).
If you have WP-CLI available to you, you could run:
wp cron event list
Though with 7mb of cron data, that can take a while, so be patient. When you figure out the action name, you can delete them all with:
wp cron event delete <action_name>
If you don’t have WP-CLI access, you can try to inspect the option value directly in the database (via phpMyAdmin or MySQL CLI), or in your database export .sql file.
I do not recommend disabling the WordPress cron as somebody else suggested here, as this will not prevent new actions from being queued, and will also break cron-dependant functionality across the entire site, including things like scheduled posts, update checks, etc.
Hope that helps.