because, generally speaking it does the job as needed, it is able to be quickly mass produced and helps to keep the cost down. If we went for a more complex design, everything else would increase. Lead times, cost, shipping costs....
It is always an option to use otehr rollers that you may find, and there are designs on printables that build off the trays. You are free to use which ones you want, but these trays have been tested with the MMU, if you use another type of roller, you might have issues.
because, generally speaking it does the job as needed, it is able to be quickly mass produced and helps to keep the cost down. If we went for a more complex design, everything else would increase. Lead times, cost, shipping costs....
It is always an option to use otehr rollers that you may find, and there are designs on printables that build off the trays. You are free to use which ones you want, but these trays have been tested with the MMU, if you use another type of roller, you might have issues.