I play a regular D&D pen and paper session weekly (5 hours a session) and have played 2nd, 3rd, 3.5, and 5th edition D&D.
I have 20 points available, then I should be able to take a score to 18. The blockage here makes no sense
Seems weird that you claim to have played 5e, and are suprised that you cannot get an ability score over 15 with point buy.