How did hockey changed over the years?

Answer 1

An answer to this question could be covered only in a book of about 500 pages

here's a few big changes since the early 20th century

1. Legalization of the forward pass

2. legalization of a one-line pass

3. phasing out of the sixth skater "Rover" position

4. positional goaltending

5. butterfly goaltending

6. the soviet system of coordinated team offense and team defense and larger reliance on horizontal play

7. an increase in offensive responsibilities for defensemen

8. bigger pads, sturdier helmets, visors

9. the instigator rule

10. the breakdown of the Soviet Union and the influx of foreign players into the NHL

11. the emergence of the US as a legitimate hockey power

12. massive expansion into non-traditional hockey markets

13. Wayne Gretzky playing for LA which indirectly affected the above two

and about 500 other things

Answer 2

hockey got more competitive