In most cases it was absolutely a financial thing. I've had some involvement in consumer hardware design over the years and pennies count. When you're making 2 Million of something, the cost of goods difference between $2 worth of electrolytic capacitors and $5 worth of Tantalum capacitors is a very significant amount of money. There are some designs that do benefit from the additional ESR of the electrolytics, but it isn't terribly common. More often that's a case of the circuit being designed around parts that were deemed "good enough", and when you use a better part, it's possible for things to not work quite right since the original design took the lower performance of the originally chosen part into account. Tantalum caps of the era were not available in as many values, and were more expensive than they are now. Ceramic caps in higher values didn't exist at all.