I do not understand why Mexico has a 100 year bond

I can think of no good reason for that long bond, and can think of a bunch of bad reasons.

Is the mexican banking regime stable for 100 years? No.
Is the Mexican legislature planning some 100 year investment project? No.
Is the 100 year bond a license for a new aristocracy? Yes.

Corruption and ignorance in the Mexican legislature seems to be the reason.

El bono de México 100 años es una muy mala idea, y sólo sirve para crear una aristocracia. Ningún régimen monetario es estable durante 100 años.

Courtesy of Zero Hedge, here is the Mexican dollar exchange rate.  Up means weaker Peso.

That is a wage cut for Mexican workers. But it is certainly a short term boost to Mexican imports into the USA. I guess the currency market thinks California won the prize in its recent federation with Mexico.  But California has no 100 year bond and no aristocracy. The Mexican ten year is 3.22%, the US ten year is 1.67%, and the California pays 2.37%.