The trouble with rolling your own headlight is that it messes with some important things:
1. The safety of others
2. Your safety
3. Liability
One of these three should mean something to you. All three matter to us. Why are each of them badly affected by improper headlights? Improper headlights are ones that are not correctly made for safety. This includes correct output (Not too bright or dim), correct beam pattern (Which is harder than it looks), and good durability (Mechanical, electrical, etc).
Most people think that brighter lights are safer. This is false. Too much light in the wrong places blinds other drivers and keeps you from seeing down the road (To the things you will hit). Bright pools of light from poorly-made lamps just light your toes instead of reaching out correctly.
Plenty of people think that the beam pattern is all about a cutoff. Also false. Many safe lights don't have a cutoff at all. Others have one. And many unsafe lamps have a very sharp cutoff. The issue is glare at driver eye level and light distribution. You need side lobes of light to see the deer on the shoulder, a center blob to see down the road, and very controlled foreground light. This can't be done with standard optics available for LEDs (Or with a utility light). The optical design to ensure this beam pattern is the main cost in headlights.
Alternators in cars put out 12VDC, with about 100V spikes thrown in for jollies. When this kills your illegal headlight, you're in the dark. This is one of the big costs in legitimate lights. The vibration and temperature environment are rough, too. Also, cheap headlight plastic ages very quickly. Very nice headlight plastic takes a few years to be no good.
Bad lights are unsafe. It's very difficult to make good lights. I couldn't do it for ten thousand dollars. Scheinwerfermann probably couldn't do it with ten thousand free either. And choosing to install unsafe lights means you are taking your safety and that of others into your own hands. And if there ever was a liability magnet better than poor choices in removing safety equipment, I'd like to see it.