The two most common excuses product people give for not producing a Product Strategy — 'I don't have time' (buried in day-to-day firefighting and whack-a-mole work, often paired with the fallback claim 'I have it in my head' or 'our plans and goals already reflect it') and 'we don't have a company-level strategy so how can I be expected to have a product one' (see What to Do When Your Company Has No Real Vision) — are rationalizations rather than real blockers.
The deeper cause is fear, of two kinds: PMs suspect, deep down, that they aren't very good at strategy, and they dread how others will receive whatever they produce (fear of rejection). The excuse-making is compared directly to a writer's block: rather than name the fear, people invent reasons why the work can't happen right now.
The prescribed fix is not a technique but a sequence: recognize the fear, accept it as the real obstacle, and only then work to combat it — instead of continuing to tell yourself you'd do strategy work if only you had more time or a clearer company strategy.