Because legal alteration refers to the processing of the criminal object by means of digging, pasting, changing, moving, reprinting and uncovering, but its basic carrier is true anyway, which is also the fundamental difference between alteration and forgery.
Therefore, letters of credit, currency, bills, etc. Obviously, it may be tampered with, but on the other hand, credit cards cannot be tampered with by digging, pasting and uncovering. If a credit card can be altered, there is actually only one situation, that is, changing the information of the magnetic stripe through technical means. But this seemingly altered behavior is actually a forgery.
For example, we can judge the authenticity of money, letters of credit and bills by appearance and anti-counterfeiting marks, but no one will judge the authenticity of a credit card by appearance. This is because the carrier of the credit card is a piece of broken plastic, which has no authenticity. It doesn't even matter whether the card itself exists or not. As long as you have the above information, you can use this card through online banking. Therefore, the only criterion to identify the authenticity of a credit card is the magnetic stripe information, and once the magnetic stripe information is changed, the credit card is completely fake, that is, forged.
Finally, the information of the letter of credit has been changed. We can confirm that the letter of credit is true through the material and appearance of the letter of credit, but the content has been changed in series, which is altered. However, the magnetic stripe information of the credit card has been changed, and we can't confirm its authenticity, so we can only assume that it is forged.