tbf I'd guess that bikram also benefits from the heat stress element, like sauna. Which is basically "free" cardio.

I'd also bet that it synergises well with yoga, as yoga is a decent mechanism for encouraging blood flow throughout the body.

I love lifting and think there are some really great elements. While ego lifting is bad, lifting a number is such a strong personal development feedback loop for most people but it's not for everyone: my partner is scared to get big, my mum and brother currently are nursing various MSK issues and can't really lift safely without serious modifications that need supervision. Meanwhile yoga, or better baduanjin (qigong) are far more accessible systems and bikram is a nice way to passively introduce extra challenge to the body and mind.