For reference, Falcon Heavy's max payloads are 63.8T to LEO and 26.7T to GTO, so today's load was quite light. ArabSat would actually have (just) fit in a regular Falcon 9 as well.
Those maximum payloads are in expendable mode, though. SpaceX wants to reduce expendable launches as much as possible. For a reusable FH the numbers are substantially lower and the satellite might not have that much more mass to still fit.