I'm no expert on this. So take this info with more than one grain of salt.
There have been several different ranking systems in the past. Some were variations of the current system. They would, for example use a different number of minimum tournaments to calculate total rank points (18 tournies, 16 tournies, etc.) The rank points looked similar to what we see today with top ten players having in the thousands of points (Jennifer at 4,800)
Other ranking methods were fundamentally different. One method would take the total number of rank points and divide by the number of tournies played to get an average number of points. Under such a system, Jennifer (the #1 player) would have maybe 500 or so points.
I don't exactly know why the system has changed over time. I think I remember reading that the tour promoters wanted to get the players to play more. Hope this helps.
The early ranking systems were "averaging" systems; total points divided by tournaments played. Usually, the only tweaking that went on was with the minimum divisor or the points allotment. In the early days, there were a lot of decimals, and your #1 player would have an average like 15.xxxxxxxxx. They later boosted the points to make the numbers easier to comprehend for the average fan. (And to make them look better.) The tour went to a "rolling 52" system in 1997, whereby the points were just added up. The complaint was that it dramatically favored those who played more. So results were capped, first at 18, then 17 tourneys. There were still complaints of the system favoring "quantity over quality", but when you consider that 1 tournament win gives you more points than 4 quarterfinal finishes, that complaint seemed groundless.
Interestingly, one of the complaints voiced last year was that the system didn't allot enough points for slam wins; "only" twice that of a Tier I. Those critics called for a return to systems similar to the past. Ironically, under one of the old systems cited as desirable, slams were only awarded 75% more points than a Tier II.