Making an OLED Lite that bridges the price gap between LCD Lite and LCD Base, in addition to the OLED Base already bridging the gap between LCD Base and Drake, that's a lot of different consoles in close price proximity that could start to get confusing for the average consumer. And being confusing to the average consumer is the sort of thing Nintendo fights to avoid.
Phasing out the LCD lineup entirely in favor of OLED on everything, to reduce power consumption and streamline orders/production? That I could see. Dunno if they'd save enough in streamlining/bulk orders to actually do it, but it's the only scenario where I'd see an OLED Lite making sense.