This is a market that continiously evolves and I do understand that at some point you have to drop/stop with developing for older models but using excuses that first we need to develop and finish the newest model before our engineers can go back to previous models doesn't help to create trust in a support dptmt.
It's called cash flow. Right now you should chose a company with good cash flow..as that will ensure more firmware. Companies which focus on current users..at the expense of the long term viability of the company..won't be producing new firmware for any model before long. Sanji don't try to generate cash flow before they have a product to sell..unlike other companies we won't mention.
So a practice you see as something to worry about (and get other users worried about!) is actually the complete opposite. If you had your way Sanji would go the way of Tvix.