The original founder of the guardian, Taylor, ran it like a business. While today journalism struggles to make money, in the 1800s news was lucrative.
In his will, Taylor carved out a sweetheart deal (right of first refusal) to sell the paper to CP Scott, a progressive Liberal politician, and also his nephew.
After running the paper for many years, CP Scott's will named his two sons to inherit. Both of whom worked as editors on the daily.
In a freak turn of events, both CP Scott and one of the sons died within a few months. The remaining son was concerned about paying double for the hefty inheritance tax at the time ("death tax").
The death tax could be so large as to force a sale of the paper, to create liquidity to cover the tax. I guess it was a tax on unrealized gains!
The remaining son, John, cleverly found a workaround to avoid the silly death tax: by renouncing his ownership and transferring the business to a Trust. Since he worked at the paper as editor, giving up ownership was a clever tradoff that actually gave him de facto tenure as editor, by making his day job more stable.
This is all to say: the guardian became a nonprofit-like trust at a point in time it was already a stable business, with capital to self-finance.
This was not a case of a independently wealthy businessman creating a foundation to create a paper from scratch (like many created universities).
The Scott trust was created by journalists for journalists, at a unique point in time where journalists had money to self-finance. Motivated not by some idealistic vision but by a more practical desire to avoid a hefty tax on unrealized gains.