Contextual advertising was used before the technology was in place for personalised ad targeting which is now standard practice.
So contextual advertising is not so much an alternative, but turning back the clock.
Advertisers somewhere will know if contextual performs as well as personalised.
One key difference between the two is the vast array of agencies, brokers and businesses earning revenur from selling, implementing, and supporting personalised advertising because it is much more complex and at least one order of magnitude more effort. This will likely impact the industry's enthusiasm for changing.