Well my take on proto-industrialization is mutli-faceted. I agree in general with Jared's analysis on low wealth, heck most of the trade systems at the time were geared towards luxury demands of the rich but a good deal of proto-industry was luxury manufacturing, the silk industry of the Po Valley was a good example of all aspects of proto-industry from individual cottages unraveling and spinning the silk to centralized and supervised workshops working mass spinning frames. On the other hand Europe pre-14th century was pretty short of silver and credit, the mediums of trade and it only improved slowly over time.
Culturally a good deal of proto-industry occurred when peasants needed to supplement their agricultural income during the off months in areas with decent market access to sell their goods. What was the climate like? If agriculture was possible all year round there wouldn't be the need to supplement incomes if work was to be found all year round.
There was also the question about children and women, what economic rights do they have? What cultural expectations are placed on them? There's a lot to go into here but an example would be French weavers during the first decades of the mechanized looms; a good deal of the early impoverished women and children that worked long hours in shitty conditions for little pay tended to be the wives and kids of weavers whom in their pride as "self-sufficient workshop owners" relied increasingly on their family to supplement their income (sometimes the only income when the weaver operated at a loss) weaving against mechanized competition and lobbying for "honest pay for honest work" in pursuit of some idealized past.
Another would be the labour rights of women, plenty of skilled women provided dirt cheap labour for early industry and guilds as those in charge classified them as "unskilled" labourers instead of the skilled work men doing the same thing did. Better rights might just dry up the labour supply.
Another example would be the property rights of women: which if one were to look at early markets a good deal of the demand for mass produced goods came from women that preferred to work in their jobs and buy everyday essentials instead of making everything themselves; in contrast to the traditional household where all of the pots, chairs, clothes, and more were self-made the women that worked and purchased helped create a massive market of millions. The net productivity may be the same but the self-sustenance household doesn't contribute to market volume or commercialization.
This also depended a lot on land-ownership agreements that varied from community to community, for example: some communities restricted their landownership to a few original families, creating large pools of seasonal labour that they can cram into monotonousness of a supervised workshop working in cramped dark places from dawn to dusk for poor pay; this was in contrast to women that spun, weaved, knitted, and socialized with their friends on their own terms and one can see the unattractiveness of "industrial work". Some communities shared land equally but required the families to farm them, this created disincentives to work in industry and bounded people to the land (since they lost a good deal of money in land ownership if they turned their backs on agriculture).
It also depended a lot on soil fertility, poor soil quality naturally leads peasants to resort to war and industry to make a living.
One of the main problems was guilds, while they maybe useful initially as allies for rulers, sources of revenue, and institutions of knowledge they tend to inevitable turn into labour aristocracies that lobbies the political powers to crush all industrial opposition so that they can maintain their monopoly, a side effect of which can be guilds soaking up all the free capital for investments. Proto-industry can't really develop when its outlawed.
There's of course the political aspects of this: you can have the church as a neglectful mass land owner like Naples, you could have the landowning nobles forbidden to participate in industry or commerce like Spain, or you could have Swabian lords that actively developed industry and forced their peasants to sell to them at low prices so that they can pocket the difference. There's countless possibilities.
Geography also plays a big role, Hungary for example was landlocked with the Danube that was barely navigatiable past the Iron Gates. It doesn't make sense for a workshop to produce 10,000 nails a day when the town only needs about 1,000 a month on an ad hoc basis, better to just have a few generalized blacksmiths. Trading was also very difficult on land, it was cheaper to ship something 100 km than it was to carry it 10 km over land; here canals helped mitigate geography but that takes time, money, desire, and expertise.
I'll tidy this up when I wake up.