2. These days one bouncer allowed per over, In 90s it used to be 2 and before that bowler used to bowl 6 bouncers in a single over.
3. Boundaries shrinking day by day in the Shorter Format, nowadays even 350 runs target is reachable, but in old times 220 was winning score.
4. Quality bats, Field restrictions, Power play, Free hit, etc
The ICC changed the rules, because according to them the audience cares more about the batsmen. The star batsmen (Virat Kohli, Steve Smith, Babar Azam.etc) have more fan following when compared to the star bowlers (Jasprit Bumrah, Mitchell Starc, Jofra Archer.etc). And in part they are right. It is the batsmen who attract the crowds, and not the bowlers. Even bowlers such as Brett Lee and Shoaib Akhtar couldn't change this. An ODI match, in which both teams score in excess of 350 will be much more well received by the crowd when compared to a match in which the average team score is 200-220.