1. The quantity of activated material in a magnetic continent fusion reactor would be orders of magnitude less than what is produced (the exhaust is not radioactive).
2. We get to close the radioactive components. It is much more manageable to put up a sign that says “No entry until 2100” than it is to put up a sign that says “No entry until 30000”. The public at large cares about this.
The "quantity" is less in the sense of amount of radioactivity. But the MASS of activated material can be very large. It's not nicely bundled up in easily removed sealed fuel elements.
The biggest problem with this radioactivity is that it renders the reactor inaccessible to hands on maintenance. Everything would have to be handled by robots. I'm reminded of how they handled that at Hanford in WW2: they demonstrated the reprocessing equipment could be maintained remotely by first assembling it remotely. I'll believe a fusion reactor can be maintained if they do the same thing and build it with robots.
2. We get to close the radioactive components. It is much more manageable to put up a sign that says “No entry until 2100” than it is to put up a sign that says “No entry until 30000”. The public at large cares about this.