I would aim to turn it mostly purple in winter, not just a little purple. That means higher light intensity. As for daylength, you could look up the seasonal variation at the Mayan archaeological zones Cobá or Chichén Itzá, in its habitat.
__________________ May the bridges I've burned light my way.
I think its the lack of watering and lighting variation through the year. You can buy a plug in timer from Kasa that will automatically turn on and off at when you sunset and sunrise occurs, which is super handy for automatically getting seasonal daylength variation. The timer is crazy cheap too. Getting the plant closer to the light would also likely help.
this plant needs full sun to do its best, in south Fla it loved full sub tropical sun, year round, no shade at all, mounted on a side of palm and otherwise ignored, all new leads bloomed with 1 flower as it is the digbyana way, A single bud per lead... no exceptions.
I grow indoors, always get blooms. I give 12 hours of artificial light in winter, full sun in summer. I use GE Grow LED Light Bulb, PAR38 Flood Light about 2 feet away, like 2-3 of them.