Before the Flavian Amphitheater (known today as the Colosseum), Games would only be held 10-12 times a year, times with religious holidays, and it was the Emperors duty to be present. Building the Flavian Amphitheater totally changed the business of holding games and they became much more frequent, so of course the Emperor wouldn't attend every single one; however, he still officiated the important games tied to holidays, commemorating famous battles, etc.