• You have an excessive number of CPU-intensive tabs open. Since most of our web browsing today happens inside dynamic web apps, all of them need to use CPU to constantly load new information.
• Because the majority of today's web browsing takes place within dynamic web apps, they all require CPU to load fresh data on a regular basis.
• You don't have any available RAM. Even though open tabs eat into your available RAM, you also have to consider all the other active processes that could cause your Mac to start throttling apps.
• Even though open tabs consume RAM, you must also consider all of the other ongoing activities that could cause your Mac to throttle programs.
• One or more of your Safari extensions isn't working properly. Extensions are the weakest link in the chain when it comes to security and stability. Make sure you only use the ones you trust and minimize their use in general.
• Make sure you only utilize the ones you trust and that you use them sparingly.
• You haven't updated your macOS to the most recent version. Safari updates are available through macOS updates, and it's always a good idea to keep up with them.

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