it´s the problem with all the other bonuses you get for free.
a +1 sword is usually a great thing. your "maximum" to hit unbuffed on level 3 is mostly +5 on attacks. getting another +1 on that is really good.
however in the game you get advantage all the time. advantage is about equal to a +5 to hit, so a +1 weapon is not as valuable anymore in that context
Not to mention the first weapon I found with an effect was a spear that gives me advantage on attack rolls against enemies I missed on the previous attack, which is pretty freaking good. All the equipment you find is already as good as if not better than a +1 weapon
