Plenty of email marketers/providers have discussed this pain point (e.g. MailChimp article), but the key idea is that Outlook uses Microsoft Word to render HTML emails. (and Microsoft Word was not optimized for that purpose)
This causes Outlook perform in unique and odd ways with different WYSIWIG editors, and there is never a one size fits all solution
What can I do if I want my emails to work perfectly in every platform, and near perfectly in Outlook?
The best suggestion we can currently advise would be to switch over to complete HTML designs, and work with a provider such as Litmus to ensure that HTML designs perform flawlessly in every platform. (and even then, different versions of Outlook render differently so it may not be perfect)
What are the repercussions of not doing customized HTML for my Outlook users?
Very low or almost non existent for most our partners, as you can see by taking a look at stats over here. Outlook is ~5% of the email market and trending downward, so this is typically not a large enough concern to warrant cost intensive design solutions.
Long term if Outlook changes their rendering approach, then their inbox may start automatically working with most WYSIWIG editors.