Dungeons and Dragons

I just looked up Fireball in 4e and 5e and while what you say isn't technically true, what you remember kind of is and shows why so many of the changes made in 4e were not well received.

While the 4e Fireball does not in fact prohibit anything to be added, it does leave out the flavor, does not explicitly mention igniting things or going around corners in the spell's text. Leaving out fluff does not encourage the player or GM to add fluff. Furthermore the 4e rules language uses the keyword system which imo is fantastic for quickly getting an overview. But it might also seem more restrictive that way and if the fluff is mentioned in the keyword descriptions then it can quickly be lost.

Now the 5e fireball does not explicitly mention or allow you do add flavor or fluff. But doing so itself it does make it clear immersion and fluff is a thing.

This same thing happens when talking about pf2e with 5e players a lot I have found. Because of pf2e having a very exact, well defined and all encompassing rules structure newcomers from 5e feel like they are more restricted and have to use every rule as written. Even though they would never do so when playing 5e. And even though the pf2e core rules explicitly state multiple times, for example in the very first paragraph, that you can and should change, leave out, add or ignore as many rules as you see fit because it's your game and your table.

In that way dnd 5e has turned one of its in my opinion main weaknesses, often incomplete or outright not balanced or working rules, into a core strength. It's modularity and adaptability is often praised when it isn't actually more modular than most systems I have run. But it requires GMs to make up shit as they go by leaving open canvasses and gaping holes ins rules, plots etc. And since a lot of the system does only loosely work together you can fit in things easily without breaking other stuff, if you got some experience.

Other systems often require you pay some more attention as balance is more tightly knit across the rule system. But in turn you are provided with clear guidelines which allow even new GMs to get balance right the first time. While in dnd 5e many of those guidelines are not given, are outdated and wrong, or never worked in the first place (for example the encounter system, no magic item prices).