filter – Difference between MS Graph API and SharePoint REST API in filtering

While working with MS Graph I noticed that if I need to filter list items by custom fields, I had to make this field indexed, or work with header attribute:

Prefer: allowthrottleablequeries
Prefer: HonorNonIndexedQueriesWarningMayFailRandomly

But if I make the same filter request with SharePoint REST API, there is no need that field has to be indexed

Please explain, why is there such a difference in approaches??