Because the board rooms of Tamiya and Trumpeter don't care what a handful of RC guys online think in comparison to their target audience of static builders, especially in a dead end scale like 1/16 (tanks are too large for normal static display). Tamiya is the creator of this entire field as a pet project, yet a majority RC users constantly knock them for being to expensive. Do you really expect them to reward that by dropping serious cash in research and development on a British tank that even history buffs would have a hard time identifying and the general public wouldn't even look at twice?

Because the Chinese toy-makers aren't going to send a crew to European museums to measure and research, to release the next $100 tank when it's easier to buy a Tamiya and measure that.

Because when a company like Xion comes out with a beautiful kit like the Kettenkrad, that everyone said they wanted, nobody bought at $200 which included El Mod, metal tracks and PE. Not to even mention the other German offerings that are often dismissed as 'too expensive', or 'one day'. Companies go bankrupt waiting for that 'one day'.

Bottom line is, money talks.

If you really want those tanks, grab yourself an existing 1/35 kit, a micrometer, calculator and a pile of styrene stock and do it. In this day and age of 3D printers and aftermarket gears, MFUs and sound cards, it should be raining Cromwells, Matildas, Lees. But it ain't.