The classic HotBits ( https://www.fourmilab.ch/hotbits/ ) uses radioactive decay to get its random data. This generates 100 bytes per second of randomness. But that also depends on getting a radiation source. A single one costs about $80. A lava lamp costs $10.
Working off the list of isotopes that they provide, You've got things that have half-lives. The issue there is that the way that one generates random data from radioactivity is get an event (A), and then get another event (B) and another event (C). The time between A and B is compared to the time between B and C. If AB is shorter than CD you've got a 1. If its longer than you've got a 0. If its the same, then throw about AB. As the material decays, its rate of generating bits of data slows down.
Lava lamps are easily replaceable and don't have half-lives.
I suspect there's also issue with "here is our lead lined vault where we keep a bunch of radioactive disks to generate random data". Sure, the units are micro Curie (the most active one is a 10uCi Cesium 137). But... do you want to go into that room and change a burnt out detector? How about swapping out a lava lamp because of a burnt out bulb?