Maybe it is available for last minute departure?
No, I am always able to get the lower points. It usually varies between 70K and 90K one way. I usually book as soon as the booking window opens. We have flown Business First (now Polaris) using the business saver points many times over the past 5 years nonstop to London, Frankfurt, Istanbul, Sydney and Auckland and now Taipei. It is not available everyday so I usually have to be a bit flexible in the travel dates to get the lower mileage. Like on this trip, we had to leave on a Friday and return on a Tuesday, except yesterday I saw some Sunday Polaris seats at an even lower point value than we are using (70K one way nonstop Polaris class Taipei to SFO). This is the first time I have been able to get Business First/Polaris class with business "saver" points at the last minute. But like I said, it was not available coming over and if we would have flown coming over on a Saturday, Economy would have cost 80K points.
I am not sure why I can get it and it is not available to you. That is very strange. Do you even see the Business Saver option when you log in?
We have the United Chase card and we spend a lot on it every year. I wonder if that has something do with it? Do you have a United Chase card?
Can you do a search for Taipei to SFO and see if you are able to see the Business Saver points I am seeing? Look on different days because it changes but you should be able to see at least something in the Business Value column.
One more thing, sometimes they do not open up Business First/Polaris until 1-2 weeks after the booking window opens. But they do open it up at least 10.5 months in advance. When the booking window opens, I check daily until the Business Saver seats show up.
With economy, I can always get economy saver seats at any time. I do not even worry about getting the economy saver anymore. I was even able to book economy saver on full flights over Thanksgiving last year to go to Cabo, although we did need to connect since it was so last minute.