There are always going to advantages and disadvantages to any particular dates chosen for the changes. (For example, there can be concerns over road safety, particularly in the north of England and Scotland, if children have to walk to or from school in the dark at the start or end of BST). So a certain amount of compromise is necessary in deciding upon the actual dates to be chosen.
The EU (whose rules we're still following in regard to daylight saving time), or EC as it was then, decided back in 1981 that the best compromise for Europe was to commence daylight saving time on the last Sunday in March. (The date for the end of DST wasn't finally fixed until 1998, having moved around a bit prior to that but eventually becoming the last Sunday in October). In coming to that decision, the EC had to take into account the vast area to be covered, from Norway in the north, to Cyprus in the south. It was never going to be perfect for every member state but, as I've indicated, it was regarded as the best compromise available.
The US authorities have similarly had to decide upon the best compromise for their own country, settling upon the second Sunday in March and the first Sunday in November.
So there's no 'scientific' reason for the choice of dates. It simply comes down to what the legislators in a particular area deem to be best for their part of the world.
If we stick to keeping our time aligned with the rest of Europe (which, from a purely practical viewpoint, such as when reading ferry and airline timetables, would seem to make a lot of sense), this year might well see the end of BST, as the EU voted back in 2019 to end DST across Europe altogether by the end of this year.