Once streets actually do have official names the naming of streets and public spaces follows certain trends and fashions that in parts change over time, and of course by country. It's people with the power to name streets who name streets, after persons or things they consider important, either for themselves or the public.

One way to name streets would be to use terms that have been in use by the population beforehand, which would usually involve names after topographic identifiers like 'Hill Street', 'Church Road', 'Wall Street', 'Lakeshore Drive' etc, but also e.g. the name of the owner of the land the street crosses (could lead to e.g. 'Hill Street' too).

Then there could be streets named after locally prominent people like the founder of the settlement or an important industry, local historians, priests etc.

And then there's what one could call 'political naming', i.e. names that are deemed to be important for the overarching society the town or city belongs to. In the US this would be e.g. 'Washington Avenue' or 'Jefferson Road', in the former USSR 'Lenin Prospekt' or 'Karl Marx Avenue', in monarchies the streets are partially named after members of the royal family, in dictatorships after important members of the party in power etc.

All this of course just scratches the surface. The bigger the city, the more streets there are, the more names you need, unless you start right away using letters and numbers.

So streets start to get named after lesser known heroes (or 'heroes'; in Germany e.g. are still a lot of 'Roon Streets', named after a prussian Minister of War hardly any german still remembers, but also streets named after people involved in Germany's short but unheroic colonial history or even after people who really nobody remembers, who turn out to be heroes of the early nazi-movement), after plants and animals, poets, actors, whatever. What it will be depends on the people who give the streets their names.

To answer the concrete part of your question:

Yonge Street is named after Sir George Yonge, 5th Baronet, who was British Secretary at War from 1782-1794: https://en.wikipedia.org/wiki/Sir_George_Yonge,_5th_Baronet

Lorne Street on the other hand was named after John Campbell, 9th Duke of Argyll, 1847-1900 known as Marquess of Lorne, resp. his wife, who was a daughter of Queen Victoria. Campbell was the 4th Governor General of Canada from 1878-1883:

https://en.wikipedia.org/wiki/John_Campbell,_9th_Duke_of_Argyll#Honours

Tl;dr: This book might be of interest for you:

Wise, Leonard/Gould, Allan: Toronto Street Names: An Illustrated Guide to Their Origins