Note that 1981 was the last year the Watchtower tied fire-walking with evil spirits, at least in print.
In 1986 Anthony Robbins, the positive thinking motivational author and speaker, published his book Unlimited Power. Robbins around this time became quite well known for his success seminars which ended with the seminar attendees fire-walking on a bed of hot coals to show that they could accomplish what they had previously might have thought was impossible.
No spiritualistic, demonic practices were involved, only positive thinking and direction by those who know how to perform fire-walking were required.
Secular fire-walking exercises showing that everyday people could indeed fire walk without getting burned are the reasons that the Watchtower hasn't made any more superstitious comments about the topic since 1981.
When something is brought out into the open, superstitions usually vanish.