Maybe the reason is it makes the tub too heavy for most homes and just getting the thing in would be a nightmare. This tub would be probably 50% heavier than the one you have. If you want this go acrylic I love acrylic tubs they are aesy to clean and easy to install without breaking someones back. efaucets has some 20" deep tubs that are are very well priced.

Kohler makes several cast iron tubs that are 21"-22" deep. However, they are indeed quite heavy and require significant manpower or a "stair climber" pneumatic lift.

Check out the Memoirs K-721 for an alcove installation.


http://www.us.kohler.com/us/Memoirs-60-x-34-alcove-bath-with-left-hand-drain/productDetail/Memoirs/419731.htm?skuId=351351&brandId=429398&pageName=globalSearch&&_requestid=3103327

You may also want to check out the Tea for Two 66 x 36
K-855-L


http://www.us.kohler.com/us/Tea-For-Two-66-x-36-alcove-bath-with-tile-flange-and-left-hand-drain/productDetail/Baths/421630.htm?skuId=374390&brandId=429431&pageName=globalSearch&&_requestid=3105274#