Ah. The biggest difference between ?/: and if/else is that ?/: is an expression (returns a value) and if/else are statements (a step/command/declaration/etc). You can build statements on top of CEL (lots do), but the core Common Expression Language (CEL) doesn't actually have them.
Note that python uses if/else for the ternary expression form as well: `a = b if c else d`
Though personally, I like to have the condition in the front, instead of in the middle.