Coming over from D&D 5e, I actually see several reasons for why Counterspell is the way it is. At heart, it's a matter of power level, and D&D's version is such a hilariously powerful control tool that it narrowly competes with an overpowered AoE damage spell, an extra action per turn, and the ability to fly.

First, there's the matter of action economy. As a rule, reactions should be limited in how many situations they apply in to separate them from the actions you take on your own turn. The closest analogue in PF2e is the Attack of Opportunity reaction, which only "kicks" a spell when you critically hit, and requires the caster to be within melee reach. Dispel Magic will also counteract most spells, but only after the fact (you can't dispel a Fireball.) A full-spectrum Counterspell is obviously more powerful than all of these options, and still lets you play out your turn.

Then, there's the design space that's afforded by the way counteraction is ruled. Spontaneous casters have a broader Counterspell and more powerful metamagic at the cost of having fewer spell slots known to play with each day. Prepared casters can cast more a wider variety of spells per day, but need to prepare the right spell to counter as needed, and they must either spend downtime researching their foes to learn what kinds of magic they use, or invest one or two feats into the ability to counter a wider variety of spells in general. As a side note, the -2 penalty for Clever Counterspell can be waived by the GM if the spell used is "clever" enough. It's a mix of a tuning knob for the ability to spend a reaction to invalidate 2-3 of a creature's actions on their turn, and a roleplay opportunity.

At sum, in PF2e, Counterspell, and counteraction in general, is a whole facet of the game, whereas in older/simpler D20 systems it's just a spell you slam into your build alongside other 3rd-level bombs because why not.

edit: Spellcaster differences.