For new graduate CS recruiting:
a. Many employers recruit at local schools out of convenience. For example, San Jose State seems to be better represented at some Silicon Valley companies than one would expect for a moderately selective non-flagship state university (though the CS major has become much more selective than the school overall, due to its popularity).
b. Larger employers are more likely to recruit widely. For example, “Google recruits here” seems to be mentioned a lot by posters mentioning a lesser known school for CS, but Google apparently recruits widely because it has need to recruit relatively large numbers of employees and has the recruiting resources to do so.
c. Some employers favor larger schools (or those with more CS majors) because traveling to recruit the 5 CS majors at some small college may not be worth it to them.
d. Non-local employers (that are not large enough to attempt to recruit at as many schools as possible) are more likely to travel to recruit at schools that they have heard about. This tends to have some relation to the prestige and reputation of the CS major more than the school overall.
Some schools may hit multiple buttons. For example, a school may be local to many companies hiring for computing jobs, be large (at least in terms of CS majors), and have a high level of prestige and reputation in CS to attract non-local employers to recruit.