It doesn’t. Those bulbs put out inadequate levels of uvb and into a very small area. By having it sideways it just slightly increases the radius that it is spread out.
@caron Coiled bulbs put out much less UVB than they claim they do. And along with that, the area it covers is very small meaning that it can big problems such as MBD or stunted growth. And yes, technically there is a use for them. They will work for animals like leopard geckos and some others. As to why they are sold, money is unfortunately the answer. That is why so many people recommend the tube lights over the compact ones. And after you purchase the light fixture, it is pretty cheap. You just have to replace the bulb every 6 months to a year. If you have YouTube, there are some good videos on why compact uvb isn’t a great option compared to other products