Some people don't really like having to adapt their champion, build, or playstyle according to their opponents. In my experience, these people seem to overlap a lot with the people who refuse to build according to the game or purchase wards.
As most mid-lane mages, 2x Doran's Rings and a Seeker's Armguard -> Zhonya's Hourglass is enough to handle laning phase. If you need mana and durability, then you can get Rod of Ages instead. If you need CDR and mana sustain, then you can typically get Chalice of Harmony -> Athene's Unholy Grail afterwards.
A lot of mid players usually take Ignite into every lane. Exhaust and Barrier are typically better options for laning against Zed so you can survive his burst to escape, discourage him from all-ining you, or bait him.
When Zed uses his ultimate, a lot of people seem to run away from his shadow instead of staying nearby even if they are capable of winning, which allows Zed to easily escape.
It may also have something to do with the champions played. For example, I like:

All of which have tools to handle assassins, especially one whose engage is as telegraphed as Zed.