Given equivalent height, a female typically has longer legs than a male but a shorter torso and arms. Consequently, an ideal fitting frame will have a shorter top tube. By utilizing 650C wheels this can be achieved, to a point, without increasing the toe clip over lap with the front wheel.

Having both wheels the same size preserves the traditional appearance, while also reducing weight. However, the reason 650C is popular with triathletes is the decreased aerodynamic drag. The smaller diameter rims are stiffer, allowing them to be built with fewer spokes. Also, it lowers the head tube, allowing for much lower handlebar and torso positions, which further reduce drag.

A lot of average size male triathletes used 650C wheels for the decreased aerodynamic drag. For instance my standard road bicycle is 56cm square (ctc) with 700c wheels. However, my triathlon/TT bicycle uses 650C wheels and has a seat tube that is 49cm (ctc), allowing for a lower aero bar and torso position.

While 650C has lower gear-inches, this is generally not a concern for the typically weaker female cyclist.

The 24" front wheels were used in cases of very short cyclists where a 24" front wheel was necessary to achieve a very short top tube without excessive toe clip to wheel overlap. Originally, it also lowered the head tube allowing for a ver6y low standover height, back when lugs were used and top tubes were horizontal. This last reason has been eliminated by the ability to use TIG welding and sloping top tubes.

Of course, you could obviously have designed around two 24" wheels. While there is a gearing concern, that is relatively easy to solve. The bigger issue was the stygma of riding what is perceived to be a child's bicycle based on the 24" wheel size. Utilizing a 27"/700C rear wheel solves both problems though introduces other issues, such as having to carry two sizes of spares.