illconditioned, yes, a good output transformer is not a cheap part, so if it can be replaced by less expensive active circuitry, the microphone can sell for less. Quality control is also faster, simpler and cheaper with transistors and other low-level components than it is with transformers, and shipping weight is enough to matter if you have 1,000-microphone batches as some manufacturers do. The budget end of the modern sales environment is competitive to the fraction of a penny, and I have no doubt that transformerless microphone circuitry has been welcomed there for this reason, particularly among far Eastern manufacturers.
Among the traditional central European manufacturers it's more a matter of history and of drastically changing times. I can tell you that Schoeps' main incentive for eliminating the transformer was technical rather than economic. The maximum SPL of the transformerless versions was one or two dB higher, depending on the model (e.g. CMT 34, 125 dB SPL; CMT 44, 126 dB SPL; CMT 54, 124 dB SPL). Those are small differences, but if a user exceeded the given maximum SPL by (say) 5 dB, particularly at low frequencies, the transformerless microphones would have markedly lower distortion than the transformer-equipped ones. When you consider what was going on in the music recording business at this time, with the rise of the Beatles and rock-n-roll in general, people were close-miking louder and louder sound sources, and the upper SPL limit was being reached much more often than it ever had been in years past. In 1973 Schoeps raised that limit to 130 dB with the introduction of the Colette series, and now that all of their new models were transformerless, that was a softer limit.
Neumann introduced their first transformerless phantom-powered microphone with a great deal of fanfare about ten years later, the TLM 170. Compared to the already existing model U 89 which used the same capsule, it had 6 dB greater headroom for the same level of sensitivity. Their catalog said that it had been possible to "reduce significantly the self-noise level of the microphone compared to similar types" and while the noise specifications for both microphones varied by some 4 dB between different catalog editions back then, the TLM 170 generally came out about 2 dB quieter.
--best regards