We are talking about the early days of electric motors here. So the understanding of physical design issues was sparse. For instance, the designer of the first Taycols, such as the Star, did not realise the importance of maintaining a closely-coupled magnetic flux circuit. The greater sophistication of specially-graded sintered carbon brushes was well into the future...

I am not sure when such carbon brushes became readily available for small motors. The critical point about them, of course, is that they offer higher resistance to the pole-to-pole short-circuit flow across the commutator as the brush bridges two sectors. This is less of an issue in the smaller motor sizes, and Taycols handled the issue in part by having large gaps between the commutator plates.
This can encourage sparking, but I think the odd Taycol practice of bathing the brushes in lubricating oil suppresses this quite effectively. The practice goes so much against the way modern motors work that few people nowadays realise the requirement, and I believe that the image of the Taycol as a major interference generator only exists because most people do not lubricate their brushes, and then wonder why they spark and wear....

And finally, of course, the Taycols are made out of readily available sheet and bar materials. Everything was made in the factory. Only the nuts and washers were bought in, and possibly the studding. Carbon brushes would have had to be bought in, and I'm not sure where you could have obtained these in the 1940s or 50s. Certainly they would have been costly items....