Because many small tech companies and startups are figuring things out as they go, there's often a "fail fast" mentality. This means that a marketer would be tasked with having a metric attached to every single one of their actions to be sure that no marketing spend is being wasted. With the rise of data-driven marketing, analytics has never been more relevant or necessary.
Marketers are often seen as secondary in importance to developers, so it's incredibly important for a tech marketer to prove his/her worth immediately. Encompassing the skills of a fullstack marketer lets a marketing hire at a small tech company be the most efficient employee possible.
Further, young and small web companies and startups often do not have the budgets to hire multiple marketing employees right away, nor do they have the bandwidth to allow employees in other realms of the company execute the technical aspects of a marketer's creative ideas. Marcelo Calubucci said it best when he wrote "it's not enough to be a brilliant marketing strategist and not know how to execute those strategies. It's not enough to have a bag full of tactical tricks if you can't create cohesion for the company positioning. A digital marketer's ability to successfully traverse the entire marketing stack means that small companies can produce marketing campaigns as effectively as larger companies, who can afford to have siloed creative and technical teams. With technical aptitudes, digital marketers not only think up their next campaigns, but they seem them through from idea, to executed strategy, to an analytical report weeks down the line.