Mac storage basics · Time Machine basics
Why does Time Machine back up so much data every time?
Short answer: It copies every changed file in full, so frequently changing big files (VMs, databases, caches, projects) inflate each backup. Exclude ones you don't need versioned.
Time Machine copies every changed file in full, so anything big that changes often makes each backup large: virtual machine images, app databases, large mail stores, caches, and media project files.
Open Time Machine's Options… and exclude things you don't need versioned hourly (VMs, caches, downloads) or that you back up another way. Fewer, bigger changes also means faster, smaller backups.