And here is another nice breakdown of the differences and various usages.
This is a tricky subject, but i honestly think a big part of the problem is related to how people get introduced to は and が. They are not really that similar once you understand the difference between “topic” and “subject” in a Japanese sentence and get use to the intentional absence of subjects in most sentences.
The trouble comes when new learners are introduced to these particles without a proper foundation in simple Japanese sentence structure and basic grammar. Unfortunately, since these are such fundamental particles, it is quite common for people to be given sentences like “watashi wa Mary desu” with an English translation of “My name is Mary” or “I am Mary” before they know what is really going on, grammatically. It is no surprise that this leads to some confusion later on when they are trying to figure out the difference between “watashi ga gakusei” and “watashi wa gakusei”.