There is a fourth possibility. That is people like FWR and NOT but each for quite different reasons. As a result, they may feel the present value of FWR alone is higher than the present value of the exchange offer. Personally, I love NOT for the much longer term, but believe FWR can be developed earlier. As well there are potentially different long term owners for each. Additionally, many may feel very leerie about how the funds will treat retail post merger. The last flow through was obviously never offered to retail.
Many FWR/NOT shareholders are diversified and wish to remain that way. As an aside, many will also predict a short term but potentially significant price drop in NOT post merger as many liquidate some or all of their newly acquired NOT shares or simply rebalance their portfolios. It is never black and white.