How do anime streaming sites decide whether to acquire licenses from studios to show their anime? What is the process of getting an anime for example onto CrunchyRoll? Let's say a new original anime airs in Japan and a lot of the viewers on the west want to watch it too.  What reasons does a streaming site consider before acquiring licenses to stream anime? How does a streaming site know what results to expect from streaming each title?
Without going into specifics, the process is the same for anime as for any other product in the world:


Is there an interest in the product? This can be measured in many different ways in case of streaming sites: polls, data analysis (who watched what, what do forums/discussion boards say), etc.
If yes, can a profit be made? (in terms of new subscribes, income from ads, etc)
If yes, is the product legal in the country you wish to sell it in? (If not, can it be made legal? Think pixelating private parts, etc)
If yes, can a license be obtained? (eg. are there no import/export restrictions)


The answers to all these questions, and a few others (technical feasibility for example - what if a series is only made in 4K and the distributor insist on not downscaling?) will enable a streaming site to make a proper business decision and either move forward with actually acquiring the license, or drop/shelve the matter.

A more comprehensive list of considerations, not specifically geared toward streaming sites but business in general, can be found on Entrepeneur, which is the most comprehensive overview of considerations going into a business decision.
Streaming sites, as a business, will ask those questions most suited to their respective fields (anime, series, movies, music, etc).