Yes, calling an election with a 20 point lead in the polls is primarily a politically opportunistic move but it is also a practical move inasmuch as PM May naturally wants the strongest possible majority going into the Brexit negotiations.

Former UK PM Cameron showed a great deal of class and respect for democracy by resigning after Brexit when he didn't have to and this would never be done here, especially by Liberal leaders who tend to leave only when forced by electoral defeat or internal revolt regardless of the good of the country.

After 2 unnecessary elections by Chretien who had a solid majority and no issue nor need but greed to call these elections more than a year short of the normal time, PM Harper later introduced a resolution that binds the government to fixed four year terms unless it has a minority and is defeated in the house.  

So is this  a flaw in the British parliamentary system or really IMHO the flaw of Liberal arrogance, authoritarianism and love of power?