Simple answer: we are trying to recruit the best employees. That means we have two competing goals:
- We want to hire well-rounded, well-educated, smart, disciplined people, and that usually means people who have graduated university with high grades
- We want to beat out all the other firms trying to do the same
How do you beat your competitors? Get there earlier! If we wait until the students are near graduation, other companies have already recruited them. And if we pull them out of school before they are done, they won't have finished the work that makes them truly well-rounded and well-educated.
A summer internship well before graduation allows us to essentially run a 10-week interview, where we can evaluate potential, and if we like what we see, we can lock them in with a guaranteed job offer when they're done. We also get all kinds of secondary benefits, like sending well-paid interns who (hopefully) had a great time working for us back into the academic pool for another year. That's word-of-mouth advertising to further build our recruitment pipeline. We also build credibility and relationships with the universities, which makes partnerships more likely. And by putting pre-graduates onto our teams, we get to inject unique perspectives and new ways of thinking.