what are the reasons twitter would request that you?

[Melody]

change your password

[Vamp]

Usually it would be because they suspect that your password has become compromised in some way.

For example, if they believe that the information has been hacked, it is better to get people to change their passwords than wait around to see if there is actually going to be a problem. Other companies have asked to people to change passwords after information has been lost. This tends to be a precautionary measure rather than anything else.