C. T. Russell explained in the Supplement to the first issue of the Watchtower in 1879 the reason for starting the magazine. Russell had been a believer and financial supporter and Associate Editor and writer and preacher in Barbour's Herald of the Morning magazine, which proclaimed that Christ had returned invisibly in 1874 and would rapture the saints in 1878. Barbour's magazine claimed that the wise virgins who would be raptured first would be the ones who were aware that Christ had indeed returned. Barbour's mission was to alert them. However, the year 1878 came and went without the rapture. Barbour and Russell had a falling out, probably over the time proofs and also the ransom, but also over business dealings. Russell decided to start his own magazine.
No other reason makes sense for this other than that Russell believed that Christ had returned in 1874 and would rapture the saints shortly, as he expected, in 1881, and that he believed it was his mission for the few years he had left on earth to tell the others who would be raptured.
Russell was still in his 20's, operated a successful men's clothing business, that grew to 5 stores, which he ran, and eventually sold for over $300,000, a lot of money in those days. Russell did not need the Watchtower for power or money, he had it already. Only a true believer would be willing to risk their money and reputation on such a cause.
For years the Watchtower did not make a profit, it had only a few subscribers, and few believers, maybe only a few hundred. Russell's initial time frame was very short - only a few years, before he would be raptured. He was not even the first president - Conley was, no doubt because he was able to contribute the most money, Russell's money was tied up in his business.
It is apparent that a true belief in the nearness of the rapture and the endtimes is highly motivating, and the feeling must be a kin to being in love. It seems to be addictive, and once the vision captures one, the intoxication is so strong that failure and disappointment often cannot destroy the belief. They get a taste of immortality and being a part of a cosmic mission, and they can't let go of it. If one date turns out to be wrong, they set other future dates.
The year 1881 came and went without the rapture. But Russell set his sights on 1914, years in the future. He had years to elaborate on a grand complex end times scenario. However, this was not the only reason for his movement. He saw the Divine Plan of the Ages as being more important, and he held to different doctrines than the mainstream, even though unorthodox, which appealed to some. If Russell had based the Watchtower solely on his chronology, it likely would have fallen apart like the Miller Movement.
The endtimes urgency eventually loses it power, and a group needs more than this to last. Belief, not power and money, is the initial motive, but as the group becomes stronger, power and money are needed to maintain the group. But belief is the driving force that keeps a religious group alive. Without the belief, a religious group can last a while on the secondary benefits, the value that results from the belief. But eventually without belief, it will die. On the other hand, a group does not grow and last for any length of time on error and abuse alone, without providing some good in return. The Bible Students/JWs lasted because it provided a framework for explaining reality, which had some measure of truth to it, and offered them a religious experience, that the believers could not find elsewhere.
While the endtimes urgency provided the fuel to start the Watchtower, it also has produced much of the warped thinking, abuses, and revisionism.