Why is fermentation of cellulose to produce biofuel and nutrients so difficult?
Your question is a little bit all over the place, but I believe I can answer it anyway. First, though, allow me to point out that your sum formula for cellulose is wrong. While glucose is indeed a single $\ce{C6}$ compound with the exhaustive sum formula of $\ce{C6H12O6}$, cellulose is, in fact, a poorly defined polymer consisting of multiple $\ce{C6H10O5}$ subunits, linked together both linearly to form long chains but also cross-linked to form extensive networks. Therefore, the better sum formula would be $\ce{(C6H10O5)_nH2O}$ or $\ce{C_{6n}H_{10n+2}O_{5n+1}}$ for very large values of $n$.

There are two reasons why glucose, its dimer maltose and its polymers amylose, amylopectin and glycogen are much more easily digested by all organisms than cellbiose (the glucose dimer that can be found in cellulose) and cellulose itself.

The first one is the type of linkage: the first set of compounds all contain &#x3b1;$\ce{{1}\bond{-&gt;}4}$ connections while cellbiose and cellulose contain &#x3b2;$\ce{{1}\bond{-&gt;}4}$ connections. This seemingly minor difference means that while the starch subunits form spirals, the cellulose subunits actually form fibres and all the enzymes designed to break up spiral subunits cannot work with fibres. 

The second is the number and type of cross-linkages. Each organism has a set of enzymes that can break up the cross-links present in amylopectin or glycogen (or both) but these again are different in shape from those in cellulose owing to the subunits’ &#x3b2; configuration in the latter.

Enzymes to break down amylose, amylopectin and glycogen are pretty much present in every multicellular organism since these compounds are used to store energy in an available form — which would not make sense if the organism could not break the storage form back down to monomers. However, cellulose was not ‘intended’ to be energy storage and thus there was no evolutionary pressure to evolve enzymes that could digest it. Therefore, only very few species that found and populated this ecologic niche are able to digest cellulose and even less are able to digest the additional compounds present in wood that makes it hard.



Now on to the process design part of your question. In general, if we have the enzymes we should be able to degrade wood to useable monomers much like whichever organisms do that in whichever environment they live. Not only the symbionts of termites are of interest but also wood-digesting fungi, naturally. However, the key difficulty here is acquiring the enzymes required in sufficient amounts to make the process economic. I am only aware of very few enzymes that can be fermented and isolated in sufficient quantities and purity to make for a possible economic use; among them a generic lipase. That is one significant hurdle process chemists must overcome.

However, there’s another bit. It may work if we have access to the enzyme but it doesn’t have to. A number of times the most significant issue for chemical engineers is the scale-up problem: reactions work fine on a small scale but once you try to scale them up to higher quantities for more throughput they break down in one way or another. I am sure without knowing the exact titles that there are shelves of books concerning the scale-up problem. To the best of my knowledge (caveat: I am not an industrial chemist or chemical engineer), it is often down to trial and error which processes work well and which don’t; and what works well for one type of product does not work at all for others.

Needless to say that one has to have access to a significant amount of funds to bridge the research gap until one actually is able to make money so it doesn’t surprise me (although I am unhappy) that the company you mention went bankrupt.