Because they are the equivalent of "fighter has unlimited casts of sword". The idea is that even when you have nothing, you always have cantrips. They were given this scaling mechanic to try and keep them damage relevant as characters leveled up. It does kind of blow low level casting away after a certain point, this is true, while martial classes don't always get similar scaling bonuses. Whether it's bad or not I feel is a matter of individual play style. Personally, post level 10 I rarely use my lower level slots for damaging spells, because I'm either upcasting low level spells or casting higher level spells.
Previous editions had cantrips using level 0 slots, and this sometimes resulted in a spellcaster being so out of magic that they could not even cast their level 0 spells. Other contemporary systems did away with cantrip slots (pathfinder orisons) and then they found their way into 4e in the form of at-will powers, then into 5e as unlimited cantrips. This came along with the 5e spellcasting changes that put a hard limit on the number of spells that you could cast per turn, and being able to only concentrate on one spell at a time. This also meant less resting abuse, as spellcasters had options when they were out of slots and could get by without long rests immediately. There's still the old stereotype of wizards begging the party to go long rest after every combat encounter.
EDIT, to say that you shouldn't be casting chromatic orb, upcast or not. It's the most cursed spell. Never cast chromatic orb.
Last edited by Piff; 21/11/20 01:45 PM.
