This is not true as a universal statement as you make it.
If you follow the DMG guidelines for treasure, and there are no ready places to buy magic items, then magic weapons are unlikely to be available for all PCs in a 5 PC party.
This used to be true, until Xanathar's guide broadly expanded access to common magical items, such as the moon-touched blade.
Edit: I should add that as a DM, I'm not... very pleased with this. It makes the resistance to non magical weapons almost meaningless. It also makes some of the magical weapons kind of... meh? Like a +1 sword isn't very exciting, but it's a
magical weapon, that counts for something. Now, less so.
On the other hand, as a player, I like it because it means that I don't "need" to find a magical sword for my warrior because I can get a budget option. That way, a player who gets their first "real" magical item and is a warrior won't be upset if it isn't a magical weapon.
So clearly, both benefits and drawbacks.
Lastly, I will mention that something
rather cool happened in a game where I am playing as a "warrior scholar" - a historian and an alchemist with such a "budget" magical sword. We started at mid levels, and my character's background is that he had learned the secret to creating a moon touched blade - a yearlong process involving elven prayers and moonlight; and had thus enchanted his own sword. Given that the item is common, it felt not too outrageous for a player who is a student of the arcane know this. The GM agreed
... a few levels later, my PC found the secret to transmuting a moon-touched blade into a
sun blade. And if you think about it, it makes sense - what is moonlight but the reflected sun?
