For simply two reasons: price and performance. Many engineers shy away from right angle designs because of the typical high cost. Two stage bevel planetary configurations can get expensive.
The Dynabox Basic servo worm can achieve up to 90:1 in a single stage and can be provided with several output options for more design versatility. This gives you back the space you need for a much lower cost.
And for super low backlash? The Dynabox Expert is perfect for quiet, precise rotary motion, limiting gear play to less than 1 arc minute.