I am expecting memory to continue reducing in future.
Of course it will. Computer code consists of lines of various instructions and actions. If you extend an app's codebase, it's only logical that it will become bigger and be made up of more characters. If you have a text file in Word, for example, on one page and you write an additional page, you can't expect that the size of the final product will be smaller or even the same as it was before. Unless they find a more efficient method to compress or shorten the code (which I doubt), the internal storage of the Nano S will continue to shrink. Those using the device can either accept that or switch to something more powerful.
Or the reason may be different, for example, Ledger adds a backdoor or something like that. We can't check because of the hidden source code. It's hard not to be paranoid about a company that has been damaging its credibility after losing its users' data. Whatever the representatives of the company say after that, the attitude towards them will never be the same.