Why does Mexico have such good foreign relations across history?

I might be biased, and if so I'm trying to dispel that, but it seems to be that Mexico historically has had very good foreign relations and if that's true I would like to know why.

You are not biased, it is actually true. Mexico is a fascinating country to study its Foreign Policy over the years. The country has a long tradition of maintaining relations with many countries, especially during the time of Lázaro Cárdenas until Adolfo López Mateos. Those years were called "The Golden Age" of Mexican foreign relations, lasting from 1934 until 1964. Afterwards, Mexico became economically liberalized and foreign relations changed as well. In many cases it is a matter of geopolitical leverage, but we will get into that later.

The best known example I think is Mexicoplatz in Austria, but then the Mexican Embassy in Tokyo is one of the most valuable buildings in the city, and people have complained that it should be given to someone else but the Japanese government has refused, apparently because of how much they appreciate the Mexican government.

Regarding Mexikoplatz in Austria, it was because Mexico was the first and sole country to publicly protest against Nazi Germany for Austria's annexation at the League of Nations in 1938.

Mexico's relations with Japan start approximately in 1610, when Mexico was a Spanish colony and due to trade relations with the Philippines and China. It was the same year that Japan sent their first visitors to Mexico. This started a 130 year long relation with Mexico.

About the building, it was given to Mexico as a token of appreciation for signing the Friendliness, Commerce and Navigation Treaty in 1888. Those were times that North-American and Western countries pressured Japan to open its market (The Opening of Japan) and was forced to sign a series of uneven treaties with them. It began in 1853 when commodore Matthew C. Perry arrived to Japan with warships in order to force their opening, which worked. (p. 5).

It was not until 1888 that Japan signed its first equal treaty with a non-Asian country, and gave Mexico the embassy in 1890. (p. 3).

It also seems that Mexico has been a safe heaven for all kinds of political refugees and still not harmed their relationship with the countries they were running from (or their enemies), like Che Guevara, the las Iranian Shah, Trotsky, among others. And why did all these people chose Mexico of all places?.

Mexico was always a safe haven for political refugees. Since Franco's dictatorship in Spain, Pinochet's dictatorship in Chile, the USSR, the Iranian Revolution. Mexico took them all because of different reasons, but most of them because of geopolitical plays, backed by the Mexican doctrines of Foreign Policy, which I will talk later.

And finally there's the fact that Mexico has the most Trade Agreements in the world, how did that even happen?, and why?, that must have been decades in the making, it must be the result of work done at least since the Revolution... but why did not other nation with larger economies and more influence, like the US or Japan, surpass Mexico on this area?

I will give a short answer for this one, but deepen it later as it is a tool for Mexico to have plenty of friendly relations with everyone. It is also important to note that many of the economical treaties are not in use due to Mexico's trade dependency on the US.

I will write a second comment with the explanation.

Edit: I will continue tomorrow as it is already late and I can't think straight anymore.