. . .so metaphorically, you become a follower of somebody or something — in this case, the global bond markets.
Rover
I agree with Rover; however, I think the metaphor goes a bit beyond this in many cases. As I usually hear the phrase used, the outcomes of the people (or businesses, entities, trends, etc.) are also tied together. The person who hitches his or her wagon to another person is usually putting some faith in that person's performance; this faith often involves some risk, is controversial, and/or is contrary to some group's expectations or advice and will ultimately impact both parties.
In the example above, the bank's leaders have put their faith in the global bond markets and, presumably, have invested (perhaps heavily) in the bonds. If those bond markets perform poorly, the bank's performance will suffer as well. There is some risk involved, and the bank has chosen to take that risk.
As another example, a head coach might put his or her faith in a controversial player (if you are a football/soccer fan, think Prandelli, Balotelli, and Di Natale). I realize Balotelli is hurt now, but let's just take a hypothetical example. Imagine that Balotelli is not injured and he is playing in the World Cup qualifiers. Also imagine that he is playing badly and is demonstrating a poor attitude on the field, but despite all of this, Prandelli keeps him in for the full 90 minutes and refuses to put Di Natale in. Let's imagine that this happens for a few games, that Italy keeps losing, and that Italian soccer fans are voicing increasing displeasure with keeping Di Natale on the bench. We can say that Prandelli has hitched his wagon to Balotelli--if Balotelli does not begin to perform at a higher level, the coach might lose his job (that is, he has tied his own outcome to the performance or outcome of another person).
The same phrase is sometimes used when a coach takes a chance on a new, less experienced or perhaps controversial player. Perhaps the coach sits a popular veteran player and starts an inexperienced player over a significant course of the season (if you have seen the movie Moneyball, think of the situation when Brad Pitt's character traded a well-known, established first baseman and started a player with no experience at first base). If the substitution is very controversial, one might say that the coach has hitched his wagon to the inexperienced player (if he does not perform well, the coach will face consequences along with the player. The player might be benched or cut from the team, and the coach might be fired).
I'm not saying the the phrase has to be used this way all the time, but it is very common, at least where I'm from. Actually, it is difficult for me to think of an example where "hitching" does not involve some kind of faith in the person or performance that could ultimately affect both parties' outcomes, so if someone else can supply one, I'd be interested.
