So if we were offered $20, all cash, just take the cash and buy shares of the acquiring company.

The problem with this scenario is that it would force a taxable event - and one would have to take an appropriate percentage of the proceeds off the table in order to pay capital gains taxes. We would be left with that much less in equivalent shares of the acquirer, assuming we would choose to purchase those shares. Plus, the price could change adversely (i.e., go higher) between the time our proceeds from the sale became available and the time they are settled for this purchase.

Better for us would be all-stock, so we don't have to be forced to pay CG taxes any sooner than we want to. This may sound like bitching at one's good fortune, but there are other factors that would be affected in our personal economies when plans have been made to sell further in the future.