Let me give you an example
A skill like teleport for the sorceress will only ever get 1 skill point.
There are many skills like this.
Give Me a reason to put 20 points into these skills.
Give me a reason to put more points into these one point wonders.
Boost the mana cost of teleport by 3 times… That will give more reason to put more than 1 point into it. 
Plus it will slow the 1point wonder/Enigma teleporters down a bit.
Actually putting more into teleport is done on rare occasion to lower mana cost, this is especially done in non-expansion D2 where mana is problematic. Yes for people with end game gear it is pointless as your + skills will be enough but it is still a slight benefit nonetheless. Doesn’t bother me, there are many one point wonders in this game that don’t benefit much from maxing out…
D2 needs more and less synergies at the same time
Less current synergies
And
More new ones based on a more logic system