Short answer is strategy.
There are a lot of variables when it comes to your PPC advertising campaign performance in no particular order:
Year | CPC | CTR | Conversion Rate | Cost Per Conversion |
2019 | $1.04 | 1.7% | 5.3% | $20 |
2018 | $1.00 | 2.2% | 3.2% | $30 |
2017 | $1.18 | 2.6% | 2.6% | $44 |