Manufacturers have been extending the support life cycle for the past few years. Samsung provides five years of updates for most phones, for example, with four years of Android updates. Still not great, but a lot better than the single year of updates you used to get.

Extremely cheap brands don't tend to do updates much, especially Android version updates.

Mid-range phones land somewhere in the middle; some have budget hardware with decent support, but other brands get good hardware for dirt cheap in exchange of basically no software support after buying the phone. The latter is great if you're planning on using custom ROMs to extend the life time of your dirt cheap hardware, but quite terrible for people who are used to buying phones four times the price and expecting the same level of support, thinking they just scored a good deal.