As an entrepreneur who has started a business and then subsequently grown it into a sustainable enterprise, I would like to expand on what Rutley has stated.
This site is not Twitter and a question such as this cannot be reduced to mere generalizations. The reason is simply because: starting something new is not that simple, it takes a certain amount of creativity and courage.
I do not pretend to be an expert in starting or building a business, but I have been involved in both these periods and comment from that background.
While the building "portion" of the exercise is indeed long on work and short on compensation, the leap taken by anybody to start a business is substantial, and frankly, far less rewarding financially than growing an existing enterprise. The professional management experts who are brought into an existing business to grow it, are highly-paid individuals entering an established business; those who start a business, undertake and endure tremendous personal risk and sacrifice.
The entrepreneurs who start up new businesses are the origin of new employment, opportunities and the essence of economic success (despite the failure rate of new businesses which gives rise to the "great risk, great reward" rule). Every thriving business that has a CEO sitting at its helm, had to be started by somebody.
This comment is not meant to detract from those who successfully build upon the work and ideas of others - but, starting a business requires a different personality, possibly more adventurous and risk-prone, than that involved in building a business. The personality traits required by the entrepreneur and the CEO are different. Trivializing one of those roles does no justice to either.
I think that the answer to Avallee's question, in essence, lies with the personality of the individual involved in the "starting" vs "building" of a business. Different skill-sets and risk-appetites are required for entrepreneurs as opposed to professional CEO's; ideas vs systems, risk vs stability, might be examples.
Both are to be admired within their field and, much like one person's personal preferences of culture or food are of an individual nature, neither is right, wrong, easier or more difficult. They are just different.