There cannot be one specific answer to this and will depend on what are driving the exclusions.
For example in the same delivery where you see the report , you can do to the audit tab and find out the exact breakdown of the exclusions.
304 Blacklisted address () - Means users have opted out 3,586 Address in quarantine () - Means delivery has failed to these emails 14,184 Double () - duplicate email address in targeting 2,820 Control group () - targeted control population to be excluded.
So in your case it will depend on what is causing the exclusion and take action accordingly.
Please note sometimes exclusion is not a bad thing to have and act as guardrails to prevent damage to brand reputation.