Problem with budget coilovers is that manufacturers make something that sells. And many buyers are misinformed what would fit their needs more or what would improve performance. So problem lies within us
Given chosen compromises within budget according to what sells there is little left for quality and performance.
If majority of customers didn't just sort shop inventory by price low to high and didn't choose ones with most knobs and in blingy paint from among first cheapest positions, most of cheapest coilovers wouldn't be that bad. Otherwise it's how it is. There are some reasonably good offerings too, eg. good struts, tein flex z/a, STs, but they are outnumbered by mirriads of crap products, so good ones are more like exception to rule. The higher budget is, the more good products with less compromises at areas that really matter can be found. Both due budget, and also because mid and high budget suspension offerings are often bought by better educated customers. So it also goes along the lines of they make what we buy and one gets what one pays for.