Maybe this "acceptable offer" is considered by Gary and other insiders as acceptable primarily as the best place to park their money over the next period of time. Remember that they all have tons of stock and need to unwind their capital gains over years, not right now. That being the case, perhaps they view First Majestic as a good home for share price appreciation (based on silver bullion increasing in 2013 and beyond plus fundamentals of FM as a company) and as other posters have stated Sprott and a few other Orko institutional funds are also heavily invested in First Majestic.
Eric Sprott is particularly super keen about silver bullion price moving strongly to the upside and I'll keep my FM shares for this reason. I'd love to see another competing offer simply to make the current FM offer get increased but we need to keep in mind that quality take over company will trump price so its a matter of who will make such a bid and how FM will respond. Its been a very long road to get here and we're all weary.