Simple or simplistic — overly easy or superficial, often with a negative nuance implying thoughtlessness.
そんな安直な方法で問題を解決できるはずがない。
You can't solve the problem with such a simplistic method.
安直な商売に手を出すと、後で痛い目を見ることが多い。
If you get involved in easy-money schemes, you often pay the price later.
企画書が安直で、説得力に欠ける。
The proposal is simplistic and lacks persuasive power.
In a dated sense: inexpensive or cheap — meaning low-cost and easy (usage is old-fashioned).
かつては安直な商品を安く売る店が多かった。
There used to be many shops selling cheap, low-quality goods.
その表現は少し安直で、今はあまり使われない。
That expression is a bit dated/cheap and is not often used now.