Exactly. We have representatives for good reasons. Almost no one cares about most bills (which means they also won't know all the intricacies that often make the difference between a good bill and a bad bill). Even with the high-profile ones that we do care about, people will often vote for what they want now instead of what they need in the longterm (though our legislators aren't much better since they constantly are looking to the next election, especially in the House). California's ballot proposition system has shown that people will vote for flawed bills that sound good and be very reluctant to ever approve tax increases.
If this were implemented, for probably 90% of votes that he casts, we would see very low turnouts with voters coming from two groups: special interests--the small group of citizens who are deeply affected by the outcome of the vote and thus find it worthwhile to vote; and political junkies who get satisfaction out of voting on every issue, but who probably don't actually have time to really be informed about every single bill, especially as they evolve.
Implementation would also be extremely challenging. How do you ensure that Oregon residents (and which residents?--those who are eligible to vote? Those who are registered to vote? All, even children, felons, etc?) can vote once, and all others cannot vote? How do you handle people whose credentials for voting (whatever they may be) are compromised? What happens when a bill is amended--do people who have already voted on it have their votes stand by default? Are they able to change them? If they're able to change them, is that at the expense of anonymity? Do you actually have anonymity anyway? How does the Senator vote if someone DoS's the voting system? And obviously if there are any security vulnerabilities in the system, lots of problems could arise. These are very hard problems; there's been quite a bit of research into evoting, yet it is still very much an unsolved problem. If someone wins on a direct democracy platform, these problems will become very apparently very fast.
Assuming successful election, a large number of people would have shown interest in this, and those people could be engaged through a variety of outlets to vote. Senators also have a sizeable budget to send mail for free to voters.
Senators have access to a list of registered voters, which could help curb fraud.