This can perhaps be understood through analysis of the passage at the beginning of tractate Berakhot. You can see there various indications for the time of the evening Shema, and it seems that the time of lying down is a sign, not the reason. If so, then even if the actual time of lying down changes nowadays, the Jewish law remains as it is.

As I recall, it can be shown from the passages at the beginning of Berakhot that this does not depend on the times of lying down and getting up, which change with time and culture.
I’ve already forgotten the proofs, but some of the discussions there that clarify the time for reciting the Shema based on the definition of day and night also point in that direction.
And one can also wonder about all the measures such as: from the time the priests enter to eat their terumah, from the time the poor person eats his bread, from the time people enter to eat their bread, and so on and so on. After all, if people enter to eat their bread at that time, then it is not a time of lying down but a mealtime. So apparently one has to say that it is a time fit for lying down, since it is already sufficiently dark, even though in the accepted culture people generally still do not go to sleep then, but are eating.
And similarly in the morning: since there is already light and one can function (“when one can recognize his friend from a distance of four cubits”), that is considered waking time, even if people are still sleeping. And as for princes, so long as the time is closer to sunrise than it is to midday, that is still the beginning of the day and counts as rising time. But if princes were to start getting up after three hours, when midday is already closer than the start of the day, that presumably would not affect the Jewish law.

Roni, that is exactly what I wrote above.

Indeed. I just expanded a bit.

In the book Responsa of Rabbi Yosef Chaim Sonnenfeld, Keren Re’em Institute, Jerusalem 2005, end of section 23:

“And I will not refrain from raising the main point, since the Torah made the matter of Shema depend on lying down and rising, and did not state the time explicitly. If ordinary human behavior changes because of the weakness that has descended upon the world, and now everyone sleeps more or gets up later, there is room to say that there is a Torah-level obligation here. And although I have not found this stated explicitly, in my humble opinion the reasoning is correct. All the more so in a place where the nature of the climate causes this. In all these cases, one may say: leave Israel to their own practice.”