They want their old territory back.
Final hair-splitting: It's not going
forwards then, it's going
backwards. It's an entitlement of a previous status quo rather than acceptance of the new one, just like the rioters being unable to accept the new status quo of
actual immigration enforcement.
The whole "we'll get
our land back" is a popular tactic in faux-nationalist (Left-wing nationalism) countries to assert state pride in the absence of action. Argentina pre-Millei, Spain with Vox, and now Mexico.
I think it comes from the contradictory nature of them being Leftist (internationalist) whilst also being Nationalist. China does the same thing with Taiwan, where despite the last 15 years of pot banging, they're no closer to mounting an actual invasion of Taiwan than when they started clamouring. Meanwhile their economy is built similarly to Fascism instead of Communism (directed corporations under "private" (selected) leadership as opposed to being owned by the workers themselves) and only seems to have achieved prosperity from being not very left-wing at all, allowing outside corporations and industries to fuck over their people with scant wages and shit safety regs. How can you be a nation that says to put its citizenry first whilst also subjecting them to shit?
A lot of these nations don't really know how to be Nationalist outside of pure rhetoric. It's an issue with Latin American countries since a shared cultural identity is relatively recent and Nationalist action would probably be of detriment to those benefiting from the current status quo, but they still need to reinforce the idea that, yes, they're
for their country and not anyone else, even if their actions don't demonstrate it at all (
such as selling land and allowing the growth of Chinese industries as opposed to your own).
A nationalist Mexico (which the current government claims it is) would want their people back from America to contribute to the betterment of the state, whilst finally putting an axe to the necks of cartels that essentially function as a parallel government — I'm sure the current administration would even lend a hand since it benefits both nations.
But no, that's too difficult, too costly, and risks attracting the ire of the cartels. Instead, it's easier to act defiant and hostile to America whilst doing absolutely nothing else to benefit the people who elected you in the first place.