Questions about diode and DPSS lasers

With DPSS lasers, the wavelength is converted, while with diode lasers, the laser is emitted directly without conversion. Now I've noticed that other than red (standard pointers) and violet (bluray player) diode lasers, most diode-based lasers (including blue, green, and yellow) are DPSS lasers, not true diode lasers. This leaves me wondering, is this due to the lasing material for other colors not being easily manufactured? Or maybe because scientists have not yet discovered a material who's properties would permit it to be used to generate the desired wavelength when used as the lasing medium for a diode laser?

And are there any blue (not violet), or green lasers out there that actually are true diode lasers, not DPSS lasers?