What are two reasons why investors in England were likely unwilling to finance the early voyages of merchants and joint-stock companies to the Americas?

There are a few reasons as to why one wouldn't want to invest in the early colonies. The most obvious being risk. Queen Elizabeth, at the beginning of this first colonial scramble, was unwilling to commit money from the national treasury in such ventures, though she had no issue with personal individuals doing so. However, even individual wealth simply wasn't enough and could easily be sunk with a ship.
Joint-stock companies do mitigate much of the risk. However, low risk doesn't mean no risk. This may not be so bad when trading along established routes or with known nations; however a colony needs much more capital investment than a trip to an already well-known port city in India to retrieve spices people know will make good money. A colony simply requires more money, and colonies in the New World didn't have as high of a success rate. Starting up a colony means starting from scratch (once again, something that costs money). You can't start growing tobacco without setting up a farm with farmers that also have everything they need to not only farm but survive, which is significantly less effort than setting up a trading post somewhere where all this already exists. If you recall, many of these early colonies didn't quite make it or had major issues early on (e.g., the missing colony of Roanoke or the starving time at Jamestown). Combine that with a lack of insurance, and whatever money put in would be lost if things went badly.
Additionally, especially after Spain basically broke their economy with their own poorly managed New World escapades, why would an English investor be as interested? Apart from maybe finding bullion, which North America had shown little of (and once again, Spain's economy tanked despite their influx of gold), there wasn't too much appeal to those wanting to make money. This was especially the case for those traveling for non-economic purposes, like religious groups (and funding a community to move because they don't like a particular church isn't much of a money-maker). Places in the east, such as China and India, were significantly more interesting. North America did have goods to offer (such as beaver or timber), but their value only became apparent later on whereas silks and spices have been coveted by Europeans since the Middle Ages. Even later on in history, America was more valuable to English business after the Revolution.
Basically, input into a venture was higher and (especially in the early days) output was less guaranteed. The monarchy didn't always help either.
https://books.google.com/books/about/The_American_Economic_History_Reader.html?id=EwHFngEACAAJ&hl=en