IIRC, not that long after WBs became popular, apartment contracts starting specifically outlawing them. Sine the bong/WB crowd are overwhelming renters that killed WBs.
There were two concerns, at the time. Per
this webpage, a queen-size water bed contains about 196 gallons, and a king-size about 235 gallons. Whether a slow (= not immediately detected) leak or a "burst" the potential for water damage to carpeting, flooring, and sub-floor is great, and not necessarily confined to one unit. With older structures, the weight-bearing ability of the floor was a concern. At 8 pounds per gallon, the math is pretty simple, and the frame adds to the weight.
Waterbeds are still around, but to the degree they are less than easy to buy, the "blame" belongs to the marketplace. Being a long-past fad, they aren't in much demand, and store owners aren't going to waste expensive showroom and storage space with slow-moving merchandise. But if that DU-member thinks it's some sort of conspiracy, he should open up a waterbed store ... if there really is large-scale pent-up demand, he should get rich very quickly.