Tech giants aren't inherently left-wing (or any other ideology, for that matter) at all. Tech giants are, at their core, for-profit operations. Look at unfettered capitalism, if you are looking for blame.
On an individual level, tech giants will (no shit, Sherlock!) evidently be shaped by both a) powerful individuals and b) market pressures and demographics.
I.e. you could be looking at a personality like Microsoft's Bill Gates. I'm actually quite fond of Bill Gates, personally, to the extent that I'm finally willing to finally forgive him for Windows 95 two decades later. Like most captains of industry, he's careful to not be too overtly political - but everything we know about him suggests he leans what a US audience would refer to as "liberal". I'd be willing to bet half a year's salary that he votes Democrat. Yet, one of his most memorable political moments was him going up against the Clinton administration in the matter of the anti-trust affair.
Consider, OTOH, someone like the new Accenture CEO Julie Sweet. Now, that woman is literally on the record as being personally close to Ted Cruz. THAT Ted Cruz, yes. Again, not on the record re. her politics but, come on, though ... And, yet, she's recognised for not only single-handedly shifting the percentage of female Tech CEOs upon her ascent but also for championing women whereever she goes.
What do they both (and all of their peers) have in common? They're quite literally measured against their ability to manage corporate performance. This doesn't make them or the corporations they lead particularly evil (or good, for that matter). It's just the job description.
Once you understand this, you'll also have to understand that the business model of both a search engine and a social media platform, abstracting somewhat but not to absurdity, is basically that of any media corporation: the "product" you sell is always going to be your end users, sold to your advertisers rather than your services, sold to your end users. Which basically boils down to: "content more relevant to your target demographic equals more users equals higher market value of your product". And that's what you'll tweak your algorithms to reflect if you've any business sense.
Long story short: it's not a conspiracy. It's the business model. Corporations don't tend to do ideology, they do profits.