Do you know that for a fact though? Clauses can be written any number of ways. "CL title in the first 2 years", "Serie A title in 2019/20", etc. Who knows exactly what the bonuses are?
First of all, the fact here is that they exist. And that puts the transfer at 50m. If when Barella leaves they are not exercised, then and only then we can claim it's a 45m transfer or whatever. But at the moment, we have committed 50m for Nicolo Barella and that's the end of the story. Just like we've committed over 80m for Romelu Lukaku. That's part of how budgeting works.
Second, the "easy" clauses tend to be related to player performance with some exceptions inlcuding the club not relegated within the next 2 seasons, participation in the Champions League for teams that automatically quality or something and other jokes of that sort*. These obviously are deal-to-deal basis and there's no template. The 'hard' clauses could be anything obviously, ranging from a number of things, some of them being unthinkable.
Third, these bonus clauses can be anything indeed. But we've seen how long it took to seal the deal despite agreeing terms with the player since freaking October! Cagliari demanded a 50m valuation and we gave it to them. They wouldn't settle for shit clauses like Barella for Ballon D'Or, 30 goals for Italy, winning the CL this season and winning the World Cup in 2022... Let's be realistic here. The clauses are related to Inter winning the Scudetto and going far in the Champions League. These CL/Europe clauses usually start paying when you reach the QF, depending on who makes the deal of course.
Fourth, you are underestimating the amount of clauses involved. The reason why we cannot know them is because there's a fuckload of them usually. Maybe we have a clause to pay Cagliari 5k per game for 150 games. Maybe there's a 100k bonus in case he doesn't play/score against Cagliari in one of the games. It could be broken to several different mini clauses that amount to 13m. The "easy" ones would be more straightforward of course, and much less in numbers. But the hard one could be broken up into 30 different clauses and only 3 of them would seem highly improbable. Meaning that we'd still end up paying over 4m of them. But since Cagliari wasn't really letting go of the whole situation, it's very likely that they have tied the bonuses to Inter's standings and European progresion. We're probably going to pay part of the clause if we end up 2nd or reach the 2nd round of the Champions League. It's not like we do that every season, so it's a hard-to-reach achievement for us. The entirety of the 5m figure would only be completed with silverware though.
*Relegation clauses are very popular in Holland for example. Which is also why people dealing with Dutch transfer insist on having relegation clauses, such as wage reduction in case of relegation if the player appears in over 75% of the games, or a penalty imposed on the club if they are relegated and the player does not feature in more than an x amount of games. And it is ridiculous as they exist in Ajax, PSV and Feyenoord contracts as well. And their agents like to add these kind of deals when their players move to mid-tier or low-tier leagues, regardless of the team's domestic quality. I was an eye witness in a situation where a difference-maker type of player was snubbed by a club (mid-tier European league) because they wouldn't accept a relegation release clause and even a drop in the playe's salay in that case. I mean, they knew there was a zero chance of relegation, but for them it was a pride thing. They felt insulted that this guy thought there was even the slightest chance of relegation! They felt cheated that he'd bring them what would have been their best player and still fear there's a chance of relegation instead of reach newer heights! Call it a cultural clash if you wish. But imagine Inter cancelling the transfer of someone like Van der Beek because his agent wanted to add a low relegation release clause