There are many spells that do not have a bigger effect when you cast them at higher level.
The description should say: This spell does this and that and and you should get this bonus when you cast it at higher level. Such as "The spell does 3d10 fire damage plus additional 1d10 for every spell level above 3."
When the spell has no extra effect at higher level the description should say: "They spell does this and it has no extra effect when you cast it by using a higher spell slot."
The PHB says you can cast spells by using a higher spell slot and the spell description shows what happens at higher levels if there is an additional effect.
I believe the writers thought it is clear that this implies there is no extra effect at higher levels when extra effects are not mentioned.
I would prefer if they use the PHB text for spells that have a bigger effect at higher levels and they add my line to spells who don´t.
Otherwise it can be very confusing. Larian should assume that not all players know the 5E rules, so its better to write some stuff instead of players having to deduce rules from information found elsewhere.

Prof. Dr. Dr. Mad S. Tist

World leading expert of artificial stupidity.
Because there are too many people who work on artificial intelligence already