It's tough for them to figure out, I'm sure.
On the one hand, with Kingdom Hall expenses at near or absolute 0, virtually all contributions to the local congregation end up being forwarded to the WTS instead of going toward electricity, water, etc.
On the other hand, without in-person meetings, it is much harder to maintain control over the flock.
On the 3rd hand, contributing via the website makes it extraordinarily easy - you can even set up recurring payments.
On the 4th hand, old-timers, the ones who tended to contribute the most, are more likely to be technophobic and not want to "send money over that danged interweb or watchamacallit". Such folks were far more likely to drop cash in the box at the KH.
Which do they value more - money or control? I'm sure it's a question they continue to wrestle with.