In business there can very often be a belief that you only need to spend the bare minimum required to keep a customer buying your product, the more passionate your customers are the less you need to spend to keep them.
This applies to FF11 and FF14, if you can spend the bare minimum and they will keep paying the sub why pay more? If you can get rid of 1-2 developers (or more) and still make around the same money, why not do that?
On a surface level this is correct, why spend $10 if $5 is all you need to spend to keep your customers engaged and paying a sub.
However Square Enix is a brand of many products, it is a company with a fanbase of very passionate people and it needs them to remain happy with them as a company. To feel the company is doing its best for them and the thing they care about.
If you run a few games as a service, very often the customers are some of your most passionate fans. If they feel the game isn't getting proper funding, and taking most of their money for profits all you're going to do is sour them to the company itself long term and make them feel as though it is their enemy.
A FF11 or FF14 player that feels as though they are being taken advantage of, are going to be far less likely to buy your other AAA games you make (specifically from the division they feel is short-changing them on the game that matters the most to them), is going to be far less likely to buy merch and is going to be far less likely to act as free advertising for all your products when you need their help the most.
Added to this, the under-investment hurts the future of those profitable games. There is less money to future proof the games, to take on new developers to keep them running past the retirement of current, or keep more casual players on-board too. FF11 makes tens of millions of dollars a year, keeping this running as long a possible should be a priority. FF14 is a very profitable game, and again the same applies.
This isn't to say FF11 and FF14 should be run at a loss, but the profit margins are obviously very very high and more could be spent on the budget to keep the customers happy and the future of the products stronger. Both games really should get more of the money they bring in put into the budget, so people can be hired to work on the game and feel more job security.
Short changing FF11 and FF14 makes short term sense to management because they make higher short term profits on the 1/4 financial reports, but it does a lot more damage to the company and the products long term success.
You can't slap extremely passionate and locked in customers in the face, and then expect them to welcome you with open arms when you bring out your next 200-300 million dollar project.