Life was not as complex when the constitution was written, and America at the time was almost entirely frontier. For context: cotton engines ("gins"), for mechanically processing the raw product were revolutionary decades after independence.

So if it l the constitution doesn't involve a lot of details, it's probably because there wasn't a lot of detail in life.

But they did understand that the country would progress and advance, and that is why they set the precedence of Amendments.

The main idea of the constitution being the way it was, was to be a framework of limitations of which general aspects of life were to remain unencumbered (for instance, never having to house the military), as well as which aspects of culture were unwelcome in general government (keeping religious specificity out of the law.)

There was no specific mention of size of government. There was mention of the most basic responsibilities of government, in regards to it being efficient at regulating that which is necessary for The People. For instance, the Post Office is mentioned specifically, because that was necessary for the people.

Essentially, it was acknowledged that some rules and institutions are necessary, because lesser analogs are inevitable. If there is no order, if there is a vacuum of administration, then another government will quickly usurp control. Toward this end, even a public post office was necessary.

This is plenty in itself to show that they were aware that government was not to be infinitesimally small, weak, or uninvolved. Emphasis was not on size, was not on "big brother", but was on By The People, For The People.

Another small window into the context and the contemporary culture, the second amendment reads:

A well regulated Militia, being necessary to the security of a free State, the right of the people to keep and bear Arms, shall not be infringed.

This clause was written at a time when public funding of permanent state level militias was not feasible. Today, arguably -- and not just by my word, but by what was the accepted understanding for about two centuries -- this clause is completely satisfied when all citizens maintain the right to join their state's "national" guard, with no more provisions necessary.

That is, when originally written, what today is called the national guard would not have been possible to organize and fund publicly. However, the amendment does not exclude the creation of a national guard. The amendment does not limit the "size of government" this way.

Size of government was not exactly the motivation of the constitution. It really was just focused on responsibility.