It's all about your body's natural response to dopamine highs and lows.
Social media, doom scrolling, candy crush, etc. are all high-dopamine activities. After you engage in these activates for a while, then stop, you're left at a relative dopamine deficiency, which your brain abhors. It attempts to rectify the deficiency by encouraging you to engage in high-dopamine activities, which you experience as being 'distracted' from the relatively low-dopamine-rewarded work you're trying to focus on. If you avoid engaging in high-dopamine activities in the morning, your brain WILL be more amenable to focus on low-dopamine-rewarded work.
Social media, doom scrolling, candy crush, etc. are all high-dopamine activities. After you engage in these activates for a while, then stop, you're left at a relative dopamine deficiency, which your brain abhors. It attempts to rectify the deficiency by encouraging you to engage in high-dopamine activities, which you experience as being 'distracted' from the relatively low-dopamine-rewarded work you're trying to focus on. If you avoid engaging in high-dopamine activities in the morning, your brain WILL be more amenable to focus on low-dopamine-rewarded work.
Read Dopamine Nation for a handy primer on this.