There were actually some ancient swords with hand protection, like the Greek kopis. But most definitely has pretty low protection. Part of it has to do with the style of fighting - swords with little hand protection were typically used alongside shields, and so you protected your hand by maneuvering the shield to intercept an opponent's blade. The development of complex hilts in Europe happened as shields were becoming less prominent due to armor, so it was likely influenced by that.

Additionally, the extra hand protection on complex hilts has its costs, like extra mass and a different balance. There's a scholagladiatoria video talking about this. Smallswords like these ones actually represent this particular trade-off - they have much less protection compared to earlier rapiers, especially against cuts, specifically because those massive hilts were a lot less convenient to carry.