It is important to keep in mind that when silicone was introduced it was the greatest thing since sliced bread.
Does that mean that previous materials were junk and everything sealed with them immediately sprung a leak? Of course not. Silicone was simply a better, longer lasting material. Also at the time more costly.
All these years later, silicone has been upstaged by even better products and silicone's luster has faded. It still does what it always did but like it's predecessors not as long or as well.
So why does the TT industry still use silicone? Most likely because it is the least expensive material that will do the job. I doubt longevity is much of a concern.