I have a uk degree and im a citizen of a commonwealth country..so why the hell cant i stay permanently in uk?

i got my BSc Biotechnology degree at cardiff university. im a sri lankan citizena nd now in sri lanka. why the hell do i need work permits,visas etc to come to uk..after all my english is fluent...im intelligent etc etc. isnt that reason enough for me to be granted permanent residence in uk?? i mean wtf..wutabout all those somali,nigerian,moroccan immigrants who arent just uneducated(most of them) but cant even cant just speak english well