I recall from past discussions on the site about its finances that theres a few major obstacles they hit;

Huge staffing costs. Not even necessarily bloat - though there is reportedly some of that - but just that they require a shitton of staff with expensive credentials to maintain and develop the site and its' backend. As the site grows, issues with code or algorithm or features require more and more resources to scale sustainably, so development snowballs similarly. It's expensive to maintain a stable of coders or developers capable of working in that scale. And not just code - their community or sales teams are also needing a lot of bodies and competitive compensation, especially up the food chain.

Hosting costs. As more and more of reddit's content is hosted in-house, their cost to deliver content has skyrocketed. There's very good business arguments to be made for keeping that content internally hosted, but those are all long-term payoff, while the costs of hosting are all much more immediate. In a prior conversation a former employee said that reddit's hosting costs have effectively kept pace with its growth in revenue.

Poor monetization, lack of vision, poor understanding of their own community.

Reddit launched without a monetization model, the plans was to build a VC darling and sell it so that monetization was someone else's problem. Now that the platform is trying to get cash positive, they've effectively failed to come up with a Plan A and gone for Plan B: ads. It's a particularly weak option, but a 'safe' fallback option used by shitty blogs and newsreels around the world. Reddit isn't offering particularly great value, it's not offering particularly great targeting, it's not even able to offer prominent placement or assured attention. Reddit is in a very poor position to sell ads when compared to Google or Facebook.

Reddit has struggled to make ads relevant, and has struggled to discover alternative revenue streams. The most major alternate revenue option has been awards / gold, but Reddit's commitment to that space has been half-assed at best, and resented or used toxically by the community at its worst. To the users or the outside world, we've never seen any attempts to make their niche more relevant to outsiders, or to make money from site users. Instead, they've waffled somewhat noncommittally in both spaces, while not excelling in either, or in walking a balance. I think it's safe to say from the Third Party Apps that there was huge willingness from Reddit's userbase to pay money in order to engage with the site in specific ways, and willingness to spend money on the community as a part of the community. Reddit never meaningfully figured out how to tap into the enthusiasm their own site inspired in its userbase.

Which I think is in large part because Reddit never really understood their own community. Reddit started with this wild anti-commercial, anti-adweb, mentality and attracted the technologically literate and internet-savvy demographic as it's core userbase, which went on to inform sitewide culture up to today. They launched a platform with anti-ad sentiment, attracted ad-opposed userbase demographics ... and then went ad-supported. This could have been something that reddit pitched successfully to the site at the time - they could have acknowledged that folks don't like ads and made a point of framing advertisers as entities choosing to support reddit and keep it free & functional - Reddit likes supporting "it's own". They could have facilitated and supported connections between advertisers and targeted communities in ways that bypass Reddit's hostility towards ads and appeals to advertisers. Instead they just started serving ads. Likewise with awards, premium, and similar: they could have done far more to play into the gamification and the willingness to support the platform - they just failed to. And today ... site Admin, Reddit Inc, have burned all of the community goodwill that could have made those programs successful by instead forcing corporate-feeling monetization and advertising upon the community.

More than wasting money directly, they've wasted opportunities and advantages. I think one huge long-term learning from Reddit's current struggle is the importance of soft skills and social acumen in managing a tech platform whose masthead product is its "communities" - they desperately needed people on staff who understood community and who understood their userbase's values and culture.