Well, first of all, there were no masks to wear. Not even enough to properly equip all medical personal. But yes, if people would wear masks whenever there is the risk that they are sick, be it Covid-19, the flu or just a cold, it would be beneficial.
You can make them yourself on a sewing machine, or even sewing by hand if you're desperate. My partner and I have made ~20 in some of our spare time in the last three weeks, for ourselves and our close family and friends. It's not high tech.
Didn't even have to go out and buy more materials.
Making your own masks is certainly something many people can do, but also many that can't. But many who can, are doing that now. And slowly the supply of commercial masks is improving here in Germany too. As the lockdown is slowly released, people will be wearing masks and that should help a lot with keeping infection numbers down. And hopefully wearing masks becomes standard now when affected by any kind of infectious disease.
Although only maybe half of the people around where I live are wearing masks of any variety, it doesn't hurt to wear a bandana or a buff or whatever when you go into a store. It probably doesn't do much good but it doesn't hurt and isn't any real effort.
