In many countries (e.g. the Schengen area) it is common for visa nationals to only receive a single entry visa for the exact duration of their trip. Supposedly it prevents the "bad guys" from overstaying and/or working undercover. However assuming one is planning to overstay, do they really care about the duration of the visa? Even if it's a single entry visa for a single day nothing stops them from throwing out their return ticket and disappearing inside the country.
So the question is - why not always issue convenient multi-entry multi-year visas to all verified travelers? Countries such as the US routinely do so despite being extremely paranoid, so it's not exactly unheard of.