This should be a hard sell. The code in production works. Why does it in need a rewrite? The fact it needed a rewrite in the first place doesn't really reflect on scrum but on poor engineering and management practices.
This might be what I have the biggest problem with. To a customer, it works. The customer is happy, they pay their money, which makes management happy, and we all get paid. So the site takes 10 seconds to load on certain pages, who cares! It works, right?
Behind the scenes, there's a fleet of web servers burning CPU so add some more! A database that's overwhelmed, throw some more CPU/mem and faster disks at it! Maybe optimise some queries if you can get it into sprint. But a fundamental problem with the implementation itself cant be fixed, because "it works". Want to leverage some slave dbs for reads? Sorry, no time for that because unpicking the backend would take too long!
It's backwards. In my idealised view: Good design first = better code = less resource hungry = less cost for servers = support more users = more revenue = less time spent working around crap = more time to implement features! = more revenue = better wages. Everyone wins.
Imho, agile doesn't help make this happen.
If you really have a fleet of web servers burning CPU and you arne't tracking the costs, then I guess "it works" until someone figures out there isn't any money left in the coffer.
There is a lot of value in working software, and unless your engineering infrastructure expenses seriously outweigh your engineering payroll costs (which does happen, but is hardly commonplace), CPU efficiency isn't the be-all to end-all and focusing on it may well prove to be counter productive. If no one actually cares about your page load times, it may very well be that it doesn't matter. You can spend a near infinite amount of time & resources trying to get optimal performance (talk to someone who does high-frequency trading to get a sense) well past the point where the costs pay off.
There is tremendous value in "it works" that engineers generally struggle to fully factor into their thinking (I come by this wisdom honestly). People have written about this extensively (e.g. https://www.joelonsoftware.com/2000/04/06/things-you-should-...). That said... the notion that you can't fix actually serious and counter-productive problems with the product because "it works" sounds not only counter to Scrum, but really counter to any software development methodology I've ever heard of.
What if the costs are fixed? (own servers, unmetered bandwidth) The problem shifts down the line when you want to add a new product and the first product is consuming all your resources. Refactoring then becomes a necessity, but there's no capacity for it because the company is focused on shiny product #2, while also adding shiny features to product #1. Now fire a few people to save money, leaving the remainder short handed, who get stressed and demoralised. But that's ok, because "it works!". Why cant we design first, lay down a good foundation, then add features. The business makes more money, people keep their jobs, instead of spit-balling "user stories" at an application which becomes a giant spit-ball.
> CPU efficiency isn't the be-all to end-all and focusing on it may well prove to be counter productive > You can spend a near infinite amount of time & resources trying to get optimal performance
I used CPU as a broad example. What happened in my case was there was no performance. At release it was unusable. What stuck in my side was I knew it was going to happen, and had been calling for refactors. But if you cant get them prioritised because you cant justify the customer benefit (it's not released yet, so nothing has fallen over yet) vs features! features! features! it then becomes a bodge job /after/ release. eg. Instead of "refactor this code to make it do fewer queries" it's "lets shove the results of these queries into a memory cache." This satisfies agile, you've iterated and made things "better" - and it fit into a 2 week sprint! - but it feels backwards.
I was going to go on and talk about quantity vs quality, but a quick fact-check google revealed the evangelists with their "Agile parables" (it even sounds cultish), which are in no way perpetuating Agile to sell support tools, say I'm wrong.
I need to thank you for making me realise it's time for a career change. After all this time Agile has failed to convince me, I'm inclined to conclude it never will. But should the next methodology of the moment come along that emphasises quality over quantity, I reserve the right to shout "I told you so!"
Again, your problem isn't coming from the methodology. The priority on quality comes from the context, not the methodology. I have a friend who does presentations on agile all the time and his team prioritizes quality pretty much over anything simply because it allows them to develop faster.
Quality got worse.
In this scenario it's the fault of agile, as the reason for doing agile was to increase quality.
It's a tool/methodology that can help you increase quality.
If quality isn't a priority, a methodology that helps to better align your work with your priorities isn't going to improve quality.