@EnderWin
1. Armor is heavy and restrictive. Their plan was to get in and out quickly, so armor would just slow them down. Plus, I assume they wore their masks outside or near the store, which is easy to conceal and they'd look like a normal person while walking to the jewelry. How can you conceal an armor? You could wear it, but damn that's suspicious. People would notice you for it and you'd be caught immediately after through witness testimony.
2. Why would there be students in a jewelry store? What was your thought process there, I'm genuinely curious. Those 2 girls are rich, but what students do you see on a daily basis with enough money to buy high class jewelry? You could make the question of 'well, if it's a popular school, why didn't they notice them?' which is valid, but not really a deterrent.
3. Assuming there were people who could fight back, such as a bodyguard for an influential person, they could just beat them. Remember that those 3 are above the norm in terms of strength, so we couldn't measure how strong the thieves were. The most likely explanation there is that they could have defeated people who were there and in the unlikely case that a strong person shows up, they'd run away.
