The 10th tropical Sign, Capricorn, is of the Element, Earth, which focuses
on the physical, rather the spiritual plane, although it is capable of spirituality.
It's of the Cardinal-modality, which encourages innovations and useful inventions.
It's competitive, and ambitious, and is a civilization-building Sign.
On the other hand, the 12th tropical Sign, Pisces, is "none-of-the-above".
So, in assessing the current Age--from the middle portion known as "the Renaissance", through the Capitalist Industrial Revolution which began in the 3rd Decant, and now, especially in its ending few degrees, the Capitalist Technological Revolution--it is obviously
not what one could reasonably expect from an Age of Pisces.
Therefore, based on the incorrect assumption that it
had to be a choice between an Age of Pisces and an early start to the Aquarian Age, the latter became the standard, Modernistic, tropical opinion.
Once you factor in the tropical Age of Capricorn (c.400 A.D.-2149 A.D.), burdened as it is with its Saturnian rulership, it makes sense that the Aquarian Age isn't yet in effect--provided one includes the Uranian rulership of the 11th tropical Sign.