There are the obvious benefits to taking the role, but here some reasons I have turned down a similar role in the past:

* By the time you're good enough to be a tech lead, you may want to venture into consulting/contracting and earn more

* You may be in a position of trading development time for managerial duties, which you may or may not enjoy

* Depending on the politics, lead dev may be just below the proverbial corporate ladder glass ceiling

* A lead dev may ultimately spend more hours working to solve a particularly challenging technical problem, which may rest on your shoulders

* You may want to work somewhere else as an 'architect'. This is a very subjective job description, but could propel you faster if your aim is to climb the HR corporate ladder

* If the development environment is lacking now for you as a senior dev, it will lack just as equally as a lead dev