right now, the possibility of lost coins leads to the risk of an incalculable profit for everybody owning bitcoins. the possibility of recycled coins on the other hand leads to the risk of an incalculable profit for everybody mining bitcoins.
so you basically want to put an awful lot of work into it and make the protocol more complex just for trading one problem that isnt really a problem for another not-really-a-problem.
thats so meaningless you could probably convince the european union to fund it

Increasing divisibility means increasing the amount of space taken up by the block chain. It's wasteful. We already have a problem with downloading the block chain as it takes days. We may very well have to increase divisibility of the existing 21 million if they become worth a great deal more. Lost coins would only compound that problem.
There is no accounting for entropy in this system. That's a problem. The reason this solution is better than increasing divisibility when needed is because this only needs to be done once.
And I'd rather make it more profitable for people doing work for the system than for people holding coins and doing nothing for it.
Think of it like a storage fee.