What if there were no more new speaker models?

I would think that most companies, regardless of what they make, would have 'research and design' people who are there to improve products and/or increase the profit margin. They may offer new lines for new target buyers; sometimes a maker of expensive gear will come out with a more 'budget-friendly' line, and vice-versa. And just because an item looks the same as an earlier one doesn't mean that incremental changes have not been made. Stagnant companies are likely to be surpassed by ones offering changes and new models. Sometimes this is good, sometimes not. 

The same reason that neck ties change sizes or collars on jackets change.  

A good example is golf equiptment. The balls and clubs have been at maximum distance for years now. If they go any further they are banned/disqualified. Yet the marketing experts continue, each year, to tell the public that "these clubs are the best/longest ever". Since the clubs are maxed out they resort to exotic looking finishes and 'must have' space age materials. The unfortunate reality is that they really won't improve your game any more than last years clubs did. They'll have you believe they will.

Marketers don't have to show proof of performance. They say whatever they want to convince you to buy. One of the tricks used is a high price tag. If it costs that much it MUST be better.  A world full of suckers will fall for it.

Is the toaster really any better than 50 years ago??? Maybe worse. Cheaper parts with planned obsolesence. It makes toast until it doesn't. That's it!

I've got another 20–30 years on this planet. Love m current speakers (Pearlacoustics Sibelius). I see no reason to ever change that and speakers should last that long.