Yeah so in an ERP platform, you (well the client) needs to pay for a feature they want to be built ontop of the platform. It may have additional tables/data structures added into the ERP system or outside of it. Sure an ERP might have say an "Field Service Module" add-on you can get. But if you're a Spa Pool shop, there might be a whole bunch of things you do spa pool specific, eg taking water chemistry measurements. With an ERP system to add say a 'chemistry tracker add-on', you're very unlikely to find one off the shelf, so you need to customise the ERP system to do it. By the end of having an ERP system that works for your Spa Pool Empire you've blown $100'000's to $millions.
The alternative is some scrappy startup does a SaaS platform for Spa Pool shops and builds the features natively. Not being hamstrung by the ERP platform, so no compromises - no UI's that look like an ugly duckling. And of course they learn every new spa pool shop that comes onboard, adapts and improves.
Eventually the SaaS software startup will become the Spa Pool system of choice, and will come up against the ERP platforms in sales pitches.
One will be ready to go for a Spa Pool shop, the other will have a team of consultants wanting to do requirements gathering....
That's the problem with ERPs, when a vertical/niche has got dedicated software, the ERPs almost always look inferior*
* Upto a certain business size/throughput/specialised requirements, then Mega Spa Pool corp is okay paying millions to have their own ERP team.